diff --git a/src/core/changes.ts b/src/core/changes.ts
index 53e85c8..26b71d2 100644
--- a/src/core/changes.ts
+++ b/src/core/changes.ts
@@ -23,7 +23,7 @@ export const EDITABLE_FIELDS = [
 ] as const;
 
 /** Inputs tracked for overrides and pending changes: the numeric cards plus 열별 본수 (an array, compared by value). */
-export const TRACKED_KEYS = [...EDITABLE_FIELDS.map((f) => f.key), 'pileRows', 'groundPosition', 'groundWaterOn', 'groundWaterEl', 'floodLevelEl', 'scourDepthM', 'highWaterEl', 'lowWaterEl', 'strataRows', 'bearingType', 'bearingLayout', 'blockRebar', 'copingRebar', 'topSplice', 'columnRebar'] as const;
+export const TRACKED_KEYS = [...EDITABLE_FIELDS.map((f) => f.key), 'pileRows', 'groundPosition', 'groundWaterOn', 'groundWaterEl', 'floodLevelEl', 'scourDepthM', 'highWaterEl', 'lowWaterEl', 'strataRows', 'bearingType', 'bearingLayout', 'blockRebar', 'copingRebar', 'topSplice', 'columnRebar', 'footingRebar'] as const;
 
 export type EditableKey = (typeof TRACKED_KEYS)[number];
 
@@ -57,6 +57,7 @@ export const FIELD_LABELS: Record<EditableKey, string> = {
   copingRebar: '코핑 배근 입력',
   topSplice: '상면 주철근 이음',
   columnRebar: '기둥 배근 입력',
+  footingRebar: '확대기초 배근 입력',
   strataRows: '지층 행',
 };
 
diff --git a/src/core/geometry.ts b/src/core/geometry.ts
index b705042..91c0e4b 100644
--- a/src/core/geometry.ts
+++ b/src/core/geometry.ts
@@ -3,6 +3,7 @@ import { buildIntegratedBlocks, type IntegratedBlock } from './integrated-block'
 import { type BlockRebarSettings, DEFAULT_BLOCK_REBAR } from './rebar/bearing-block';
 import { type CopingRebarSettings, DEFAULT_COPING_REBAR, DEFAULT_TOP_SPLICE, type TopSpliceSettings } from './rebar/coping-settings';
 import { type ColumnRebarSettings, DEFAULT_COLUMN_REBAR } from './rebar/column-settings';
+import { type FootingRebarSettings, DEFAULT_FOOTING_REBAR } from './rebar/footing-settings';
 import { layoutText, resolveRowCounts, rowLayout, type PileGeometry } from './piles';
 import type { PierInput, Row } from './types';
 import { type CopingGeom, P1_COPING_GEOM } from './coping-geom';
@@ -184,6 +185,8 @@ export interface PierModel {
   topSplice: TopSpliceSettings;
   /** 기둥 배근 입력 used by the column rebar (승인 2026-10-26). */
   columnRebar: ColumnRebarSettings;
+  /** 확대기초 배근 입력 used by the footing rebar (승인 2026-10-26). */
+  footingRebar: FootingRebarSettings;
   columns: ColumnModel[];
   footings: FootingModel[];
   blindings: BlindingModel[];
@@ -475,6 +478,7 @@ export function buildPier(input: PierInput): PierModel {
     copingRebar: { ...DEFAULT_COPING_REBAR, ...input.copingRebar },
     topSplice: { ...DEFAULT_TOP_SPLICE, ...input.topSplice },
     columnRebar: { ...DEFAULT_COLUMN_REBAR, ...input.columnRebar },
+    footingRebar: { ...DEFAULT_FOOTING_REBAR, ...input.footingRebar },
     columns,
     footings,
     blindings,
diff --git a/src/core/rebar/column.ts b/src/core/rebar/column.ts
index 33ebd9f..5a7380f 100644
--- a/src/core/rebar/column.ts
+++ b/src/core/rebar/column.ts
@@ -2,12 +2,15 @@ import type { PierModel } from '../geometry';
 import { DEFAULT_MATERIAL, developmentLength, fyOf, hookLength, Material, NOMINAL_DIAMETER, spliceLength } from './common';
 import { layers } from './footing';
 import { DEFAULT_COLUMN_REBAR } from './column-settings';
+import { DEFAULT_FOOTING_REBAR, type FootingRebarSettings } from './footing-settings';
 
 /**
  * 기둥 철근 C4 (plan C4). Source: RAG/기둥철근 (1).md, 2026-10-22 최종 정리. Type-1 원형 중실 기둥.
  * Lengths in mm, heights in mm from the 확대기초 상면 (up +).
  */
 export interface ColumnInput {
+  /** 확대기초 배근 입력 (층 높이·띠철근 기준). Absent = the defaults. */
+  footing?: FootingRebarSettings;
   /** 기둥 지름 D. */
   D: number;
   /** 기둥 높이 H_c (확대기초 상면 ~ 코핑 Level 하면). */
@@ -55,7 +58,7 @@ export function columnInputFor(model: PierModel, base: ColumnInput = COLUMN_P1):
   const eP1 = Math.round((seg.top - (c3 - 0.1)) * 1000);
   // e_top: the coping middle level (Level 하면 + 계단 상면)/2 is the top of P3 and P6 (승인 2026-10-23).
   const eTop = Math.round((seg.top - (model.levelBottom + seg.top) / 2) * 1000);
-  return { ...base, ...model.columnRebar, Hc, hcop, eP1, eTop, D: model.columnDiameterMm };
+  return { ...base, ...model.columnRebar, footing: model.footingRebar, Hc, hcop, eP1, eTop, D: model.columnDiameterMm };
 }
 
 export const COLUMN_P1: ColumnInput = {
@@ -94,8 +97,8 @@ export function deleteInterferingP4(p4: number[], topBars: TopBar[], dP4: number
 }
 
 /** Top-layer bars of the footing as heights from its 상면 (B5 and B1, §4.2). */
-export function footingTopBars(Hf: number): TopBar[] {
-  const z = layers(Hf);
+export function footingTopBars(Hf: number, f: FootingRebarSettings = DEFAULT_FOOTING_REBAR): TopBar[] {
+  const z = layers(Hf, f);
   return [
     { name: 'B5', z: z.B5 - Hf, d: NOMINAL_DIAMETER.S29 },
     { name: 'B1', z: z.B1 - Hf, d: NOMINAL_DIAMETER.S25 },
@@ -115,7 +118,7 @@ export function columnRebar(x: ColumnInput = COLUMN_P1, m: Material = DEFAULT_MA
   const lD2 = developmentLength(dS32, fyOf(m, 'S32'), m.fck);
   const zTop2 = x.Hc + lD2;
   // Bottom of P1 and P2: 확대기초 하면 2단 (B7) 위 + (d_B7 + d_P1)/2 (기둥철근.md §3.2, the same for both).
-  const zBot = -x.Hf + layers(x.Hf).B7 + (NOMINAL_DIAMETER.S19 + dS32) / 2;
+  const zBot = -x.Hf + layers(x.Hf, x.footing ?? DEFAULT_FOOTING_REBAR).B7 + (NOMINAL_DIAMETER.S19 + dS32) / 2;
   // Couplers at k·ctc from the footing, kept at least the margin below the P1 top (커플러 여유).
   const couplerMargin = x.couplerTopMargin ?? 2500;
   const couplerCount = Math.max(0, Math.floor((zTop1 - couplerMargin) / x.ctcCoupler));
@@ -145,7 +148,7 @@ export function columnRebar(x: ColumnInput = COLUMN_P1, m: Material = DEFAULT_MA
   const z5last = lE - n5all * x.ctcP5;
   const m4 = Math.floor((z5last + x.rP4 * x.Hf) / x.ctcP4);
   const p4All = Array.from({ length: m4 }, (_, j) => z5last - (j + 1) * x.ctcP4);
-  const p4Check = deleteInterferingP4(p4All, footingTopBars(x.Hf));
+  const p4Check = deleteInterferingP4(p4All, footingTopBars(x.Hf, x.footing ?? DEFAULT_FOOTING_REBAR));
   const p4 = p4Check.kept;
 
   // P6 crossties (기둥철근.md §7): 4 bars per 단, from the first kept P4
diff --git a/src/core/rebar/footing-settings.ts b/src/core/rebar/footing-settings.ts
new file mode 100644
index 0000000..8033277
--- /dev/null
+++ b/src/core/rebar/footing-settings.ts
@@ -0,0 +1,68 @@
+/**
+ * 확대기초 배근 입력 (승인 2026-10-26, 시안 ③ 확대기초). The editable inputs of the 확대기초 panel.
+ * Defaults are the 확대기초철근 (1).md values; the ranges are proposed and pending the design-standard check.
+ * Fixed values (k = 2, Δ₂ = 100, 전단 4s · 엇갈림 2s, cycle 교대 배치) are not inputs.
+ */
+export interface FootingRebarSettings {
+  /** 상면 피복 (최외측 철근 중심까지, mm). */
+  cTop: number;
+  /** 측면 피복 (mm). */
+  cSide: number;
+  /** 하면 피복 (mm). */
+  cBottom: number;
+  /** 첫 철근 최소 여유 (측면 피복 다음, mm). */
+  eMin: number;
+  /** 격자 실간격 s (mm). */
+  s: number;
+  /** B10 높이 간격 s_v (mm). */
+  sV: number;
+  /** B5 아래 최소 여유 e_top (mm). */
+  eTop: number;
+  /** 조립 단 배수 n (조립 단 간격 = n·s_v). */
+  n: number;
+}
+
+export const DEFAULT_FOOTING_REBAR: FootingRebarSettings = {
+  cTop: 100,
+  cSide: 100,
+  cBottom: 150,
+  eMin: 150,
+  s: 125,
+  sV: 200,
+  eTop: 150,
+  n: 2,
+};
+
+/** Allowed range per input (inclusive, mm; n is a count). */
+export const FOOTING_REBAR_RANGES: Record<keyof FootingRebarSettings, [number, number]> = {
+  cTop: [80, 150],
+  cSide: [80, 150],
+  cBottom: [100, 200],
+  eMin: [100, 200],
+  s: [100, 150],
+  sV: [150, 250],
+  eTop: [100, 200],
+  n: [1, 3],
+};
+
+export interface FootingSettingsIssue {
+  code: 'FT01' | 'FT02';
+  key: keyof FootingRebarSettings;
+  message: string;
+}
+
+/** FT01: a value is not a finite number or is out of range (W). FT02: the 조립 단 배수 n is not an integer. */
+export function footingSettingsIssues(s: FootingRebarSettings): FootingSettingsIssue[] {
+  const out: FootingSettingsIssue[] = [];
+  for (const key of Object.keys(FOOTING_REBAR_RANGES) as (keyof FootingRebarSettings)[]) {
+    const v = s[key];
+    const [lo, hi] = FOOTING_REBAR_RANGES[key];
+    if (!Number.isFinite(v) || v < lo || v > hi) {
+      out.push({ code: 'FT01', key, message: `FT01 ${key} ${v} 범위 밖 (${lo}–${hi})` });
+    }
+  }
+  if (Number.isFinite(s.n) && !Number.isInteger(s.n)) {
+    out.push({ code: 'FT02', key: 'n', message: `FT02 조립 단 배수 ${s.n}는 정수여야 합니다` });
+  }
+  return out;
+}
diff --git a/src/core/rebar/footing.ts b/src/core/rebar/footing.ts
index e102e09..be4625d 100644
--- a/src/core/rebar/footing.ts
+++ b/src/core/rebar/footing.ts
@@ -1,26 +1,15 @@
 import { hookLength, NOMINAL_DIAMETER, type BarSize } from './common';
+import { DEFAULT_FOOTING_REBAR, type FootingRebarSettings } from './footing-settings';
 
 /**
  * 확대기초 철근 B1–B8, B10–B12 (plan C5). Source: RAG/확대기초철근 (1).md, 2026-10-22 최종 정리.
  * B9 (전단철근) is not computed yet. Lengths in mm, heights in mm from the 확대기초 하면.
  */
-export const FOOTING_DEFAULTS = {
-  /** 피복 상면 / 측면 / 하면 (최외측 철근 중심까지). */
-  cTop: 100,
-  cSide: 100,
-  cBottom: 150,
-  /** 첫 철근 최소 여유. */
-  eMin: 150,
-  /** 격자 실간격 s. */
-  s: 125,
-  /** 하면 1단과 2단의 간격 Δ_2. */
-  delta2: 100,
-  /** B10 높이 간격 s_v and 조립 단 배수 n. */
-  sV: 200,
-  n: 2,
-  /** 상단 최소 여유 e_top (B10 top level, §7.1). */
-  eTop: 150,
-} as const;
+/** 확대기초 고정 규칙 (사양): Δ₂ 하면 1·2단 간격 = 100 (고정). The other values are the editable defaults. */
+export const DELTA2 = 100;
+
+/** Kept for reference; the calculations read the settings passed in (승인 2026-10-26). */
+export const FOOTING_DEFAULTS = { ...DEFAULT_FOOTING_REBAR, delta2: DELTA2 } as const;
 
 export interface GridResult {
   /** 격자 칸 수 n = floor((A − 2·e_min)/s); 위치 수 = n + 1. */
@@ -34,10 +23,10 @@ export interface GridResult {
 }
 
 /** Grid along one side of the footing (§3.1). side = W for B1–B4, L for B5–B8. */
-export function grid(side: number, s: number = FOOTING_DEFAULTS.s, cSide: number = FOOTING_DEFAULTS.cSide, eMin: number = FOOTING_DEFAULTS.eMin): GridResult {
-  const A = side - 2 * cSide;
-  const n = Math.floor((A - 2 * eMin) / s);
-  const G = n * s;
+export function grid(side: number, f: FootingRebarSettings = DEFAULT_FOOTING_REBAR): GridResult {
+  const A = side - 2 * f.cSide;
+  const n = Math.floor((A - 2 * f.eMin) / f.s);
+  const G = n * f.s;
   const e = (A - G) / 2;
   return { n, G, e, positions: n + 1 };
 }
@@ -57,18 +46,17 @@ export interface Layers {
   B7: number;
 }
 
-export function layers(H: number): Layers {
-  const { cTop, cBottom, delta2 } = FOOTING_DEFAULTS;
-  const zB5 = H - cTop;
+export function layers(H: number, f: FootingRebarSettings = DEFAULT_FOOTING_REBAR): Layers {
+  const zB5 = H - f.cTop;
   const zB1 = zB5 - (d('S29') + d('S25')) / 2;
-  const zB24 = cBottom;
-  const zB68 = cBottom + (d('S25') + d('S29')) / 2;
-  return { B5: zB5, B1: zB1, B24: zB24, B68: zB68, B3: zB24 + delta2, B7: zB68 + delta2 };
+  const zB24 = f.cBottom;
+  const zB68 = f.cBottom + (d('S25') + d('S29')) / 2;
+  return { B5: zB5, B1: zB1, B24: zB24, B68: zB68, B3: zB24 + DELTA2, B7: zB68 + DELTA2 };
 }
 
 /** Lengths of the B1–B4 family along the length L (§5.2). */
-export function legB2(H: number): number {
-  const z = layers(H);
+export function legB2(H: number, f: FootingRebarSettings = DEFAULT_FOOTING_REBAR): number {
+  const z = layers(H, f);
   return z.B1 - z.B24; // 1723 at H 2000
 }
 
@@ -82,13 +70,13 @@ export interface FootingBar {
 }
 
 /** B1–B4 (§5): the grid along W, with lengths from L. */
-export function bottomBars(L: number, W: number, H: number): FootingBar[] {
-  const g = grid(W);
+export function bottomBars(L: number, W: number, H: number, f: FootingRebarSettings = DEFAULT_FOOTING_REBAR): FootingBar[] {
+  const g = grid(W, f);
   const n = g.positions;
   const N4 = Math.ceil(n / 2); // B4 at even i
   const N2 = Math.floor(n / 2); // B2 at odd i
-  const l0 = L - 2 * FOOTING_DEFAULTS.cSide;
-  const leg2 = legB2(H);
+  const l0 = L - 2 * f.cSide;
+  const leg2 = legB2(H, f);
   return [
     { name: 'B1', size: 'S25', count: N2, length: l0 + 2 * legLength('S25') },
     { name: 'B2', size: 'S25', count: N2, length: l0 + 2 * leg2 },
@@ -98,13 +86,13 @@ export function bottomBars(L: number, W: number, H: number): FootingBar[] {
 }
 
 /** B5–B8 (§6): the grid along L, with lengths from W. */
-export function crossBars(L: number, W: number, H: number): FootingBar[] {
-  const g = grid(L);
+export function crossBars(L: number, W: number, H: number, f: FootingRebarSettings = DEFAULT_FOOTING_REBAR): FootingBar[] {
+  const g = grid(L, f);
   const n = g.positions;
   const N8 = Math.ceil(n / 2); // B8 at even i
   const N6 = Math.floor(n / 2); // B6, B5, B7 at odd i
-  const l0 = W - 2 * FOOTING_DEFAULTS.cSide;
-  const z = layers(H);
+  const l0 = W - 2 * f.cSide;
+  const z = layers(H, f);
   const leg6 = z.B5 - z.B68;
   return [
     { name: 'B5', size: 'S29', count: N6, length: l0 + 2 * legLength('S29') },
@@ -115,19 +103,19 @@ export function crossBars(L: number, W: number, H: number): FootingBar[] {
 }
 
 /** B10 levels: m = floor((z_B5 − e_top − c_b)/s_v) (§7.1), so the count is m + 1 (9 for P1, H 2000). */
-export function b10Levels(H: number): number {
-  const m = Math.floor((layers(H).B5 - FOOTING_DEFAULTS.eTop - FOOTING_DEFAULTS.cBottom) / FOOTING_DEFAULTS.sV);
+export function b10Levels(H: number, f: FootingRebarSettings = DEFAULT_FOOTING_REBAR): number {
+  const m = Math.floor((layers(H, f).B5 - f.eTop - f.cBottom) / f.sV);
   return m + 1;
 }
 
 /** Depth of a side bar from the side face: c_s + (d_a + d_b)/2 (§7, §8.3). B10-1 hangs on B6, B10-2 on B2. */
-export const sideDepth = (dOuter: number, dB10: number) => FOOTING_DEFAULTS.cSide + (dOuter + dB10) / 2;
+export const sideDepth = (dOuter: number, dB10: number, f: FootingRebarSettings = DEFAULT_FOOTING_REBAR) => f.cSide + (dOuter + dB10) / 2;
 
 /** B10-1 (on W sides) and B10-2 (on L sides): m + 1 levels at s_v, two faces each (§7). */
-export function sideBars(L: number, W: number, H: number): FootingBar[] {
-  const depth1 = sideDepth(NOMINAL_DIAMETER.S29, NOMINAL_DIAMETER.S19); // B10-1: 123.85
-  const depth2 = sideDepth(NOMINAL_DIAMETER.S25, NOMINAL_DIAMETER.S19); // B10-2: 122.25
-  const levels = b10Levels(H);
+export function sideBars(L: number, W: number, H: number, f: FootingRebarSettings = DEFAULT_FOOTING_REBAR): FootingBar[] {
+  const depth1 = sideDepth(NOMINAL_DIAMETER.S29, NOMINAL_DIAMETER.S19, f); // B10-1: 123.85
+  const depth2 = sideDepth(NOMINAL_DIAMETER.S25, NOMINAL_DIAMETER.S19, f); // B10-2: 122.25
+  const levels = b10Levels(H, f);
   const hook = hookLength('main90', d('S19'));
   return [
     { name: 'B10-1', size: 'S19', count: levels * 2, length: L - 2 * depth2 + 2 * hook },
@@ -136,10 +124,10 @@ export function sideBars(L: number, W: number, H: number): FootingBar[] {
 }
 
 /** Assembly levels j = n, 2n, … strictly inside the B10 levels, 0 < j < m (§8.1). */
-export function assemblyJs(H: number): number[] {
-  const m = b10Levels(H) - 1;
+export function assemblyJs(H: number, f: FootingRebarSettings = DEFAULT_FOOTING_REBAR): number[] {
+  const m = b10Levels(H, f) - 1;
   const js: number[] = [];
-  for (let j = FOOTING_DEFAULTS.n; j < m; j += FOOTING_DEFAULTS.n) js.push(j);
+  for (let j = f.n; j < m; j += f.n) js.push(j);
   return js;
 }
 
@@ -149,21 +137,21 @@ export function assemblyEndOffset(): number {
 }
 
 /** B11 (along W, between the B10-2 levels) and B12 (along L), 4s apart with a 2s stagger per level (§8). */
-export function assemblyBars(L: number, W: number, H: number): FootingBar[] {
-  const levelsJ = assemblyJs(H);
+export function assemblyBars(L: number, W: number, H: number, f: FootingRebarSettings = DEFAULT_FOOTING_REBAR): FootingBar[] {
+  const levelsJ = assemblyJs(H, f);
   const perLevel = (n: number, startOdd: number, startEven: number) =>
     levelsJ.map((_, idx) => {
       const i0 = idx % 2 === 0 ? startOdd : startEven;
       return Math.floor((n - i0) / 4) + 1;
     });
-  const nW = grid(W).positions - 1; // 61
-  const nL = grid(L).positions - 1; // 79
+  const nW = grid(W, f).positions - 1; // 61
+  const nL = grid(L, f).positions - 1; // 79
   // B11 is spread along L (n = 79) and B12 along W (n = 61); each level has its own count.
   const b11 = perLevel(nL, 0, 2).reduce((a, b) => a + b, 0);
   const b12 = perLevel(nW, 0, 2).reduce((a, b) => a + b, 0);
   const hook = Math.round(hookLength('main90', d('S16'))); // 246 mm, rounded as in the document (§8.3)
-  const depth1 = sideDepth(NOMINAL_DIAMETER.S29, NOMINAL_DIAMETER.S19);
-  const depth2 = sideDepth(NOMINAL_DIAMETER.S25, NOMINAL_DIAMETER.S19);
+  const depth1 = sideDepth(NOMINAL_DIAMETER.S29, NOMINAL_DIAMETER.S19, f);
+  const depth2 = sideDepth(NOMINAL_DIAMETER.S25, NOMINAL_DIAMETER.S19, f);
   return [
     { name: 'B11', size: 'S16', count: b11, length: W - 2 * (depth1 + assemblyEndOffset()) + 2 * hook },
     { name: 'B12', size: 'S16', count: b12, length: L - 2 * (depth2 + assemblyEndOffset()) + 2 * hook },
@@ -171,9 +159,9 @@ export function assemblyBars(L: number, W: number, H: number): FootingBar[] {
 }
 
 /** Plane positions of the grid along one side, mm from the footing centre: x_i = −side/2 + c_s + e + i·s (§3.1). */
-export function gridPositions(side: number): number[] {
-  const g = grid(side);
-  return Array.from({ length: g.positions }, (_, i) => -side / 2 + FOOTING_DEFAULTS.cSide + g.e + i * FOOTING_DEFAULTS.s);
+export function gridPositions(side: number, f: FootingRebarSettings = DEFAULT_FOOTING_REBAR): number[] {
+  const g = grid(side, f);
+  return Array.from({ length: g.positions }, (_, i) => -side / 2 + f.cSide + g.e + i * f.s);
 }
 
 /** B9 bar of the rule (§9.1, Q-B18): a vertical bar at (x, n), mm from the footing centre. */
@@ -187,9 +175,9 @@ export interface B9Bar {
  * starts at 1 (even r) or 3 (odd r) and steps by 4. A bar is left out when it falls in a column zone: its centre is closer
  * than the column radius plus half a bar to a column axis (Q-B20, applied: the 기둥 구역 is removed).
  */
-export function b9Bars(L: number, W: number, columnX: number[], columnD: number = 2000): { rows: number; perRow: number[]; bars: B9Bar[] } {
-  const xs = gridPositions(L);
-  const ns = gridPositions(W);
+export function b9Bars(L: number, W: number, columnX: number[], columnD: number = 2000, f: FootingRebarSettings = DEFAULT_FOOTING_REBAR): { rows: number; perRow: number[]; bars: B9Bar[] } {
+  const xs = gridPositions(L, f);
+  const ns = gridPositions(W, f);
   const rowIndices: number[] = [];
   for (let i = 1; i < ns.length; i += 4) rowIndices.push(i);
   const halfBar = NOMINAL_DIAMETER.H16 / 2;
@@ -213,9 +201,9 @@ export function b9Bars(L: number, W: number, columnX: number[], columnD: number
  * B9 전단철근 (확대기초철근 (1).md §9). Vertical bars from the B2·B4 level to the B5 level, H16, with 135° hooks at both ends.
  * Length = l_v + 2·l_h (l_v = z_B5 − z_B24). The hook tail (6·d) turns toward the footing centre (Q-B19, applied).
  */
-export function shearB9(L: number, W: number, H: number, columnX: number[] = [], columnD: number = 2000): { rows: number; perRow: number[]; count: number; length: number; bars: B9Bar[] } {
-  const { rows, perRow, bars } = b9Bars(L, W, columnX, columnD);
-  const lv = layers(H).B5 - layers(H).B24; // 1750
+export function shearB9(L: number, W: number, H: number, columnX: number[] = [], columnD: number = 2000, f: FootingRebarSettings = DEFAULT_FOOTING_REBAR): { rows: number; perRow: number[]; count: number; length: number; bars: B9Bar[] } {
+  const { rows, perRow, bars } = b9Bars(L, W, columnX, columnD, f);
+  const lv = layers(H, f).B5 - layers(H, f).B24; // 1750
   const lh = hookLength('stirrup135', d('H16'));
   return { rows, perRow, count: bars.length, length: lv + 2 * lh, bars };
 }
@@ -237,11 +225,9 @@ export function legOffsets(): { B1: number; B3: number; B5: number; B7: number }
 }
 
 /** B11/B12 heights (§8.1): B10 levels at 150 + k·s_v; the assembly levels are j = n, 2n, 3n (n = 2), and B12 sits d_B10 above B11. */
-export function assemblyHeights(H: number): { B11: number[]; B12: number[] } {
-  const { cBottom } = FOOTING_DEFAULTS;
-  const sV = FOOTING_DEFAULTS.sV;
-  const js = assemblyJs(H);
-  const B11 = js.map((j) => cBottom + j * sV);
+export function assemblyHeights(H: number, f: FootingRebarSettings = DEFAULT_FOOTING_REBAR): { B11: number[]; B12: number[] } {
+  const js = assemblyJs(H, f);
+  const B11 = js.map((j) => f.cBottom + j * f.sV);
   const B12 = B11.map((z) => z + NOMINAL_DIAMETER.S19);
   return { B11, B12 };
 }
diff --git a/src/core/rebar/summary.ts b/src/core/rebar/summary.ts
index 88cf10f..a0f52ee 100644
--- a/src/core/rebar/summary.ts
+++ b/src/core/rebar/summary.ts
@@ -2,6 +2,7 @@ import type { PierModel } from '../geometry';
 import { barLength, bearingBlockRebar, DEFAULT_BLOCK_REBAR, totals } from './bearing-block';
 import { DEFAULT_COPING_REBAR } from './coping-settings';
 import { DEFAULT_COLUMN_REBAR } from './column-settings';
+import type { FootingRebarSettings } from './footing-settings';
 import { bottomPiece, topBarLength, widthLayout, topSplicePieces } from './coping-main';
 import { shearBars, shearBarsMulti, copingSideBars, SIDE_HOOK_LEG, c14Bars, c14Length, stairBars, stepDevLength, undersideAt, shearULength, capLength, PIECES_PER_POSITION } from './coping';
 import { sideRowLevels } from '../coping-geom';
@@ -105,13 +106,13 @@ interface FootingBar {
 }
 
 /** The footing bars of one footing (B1–B12 and B9), with the notes used in the 철근표. */
-function footingBarList(Lf: number, Wf: number, Hf: number, columnX: number[]): FootingBar[] {
+function footingBarList(Lf: number, Wf: number, Hf: number, columnX: number[], f: FootingRebarSettings): FootingBar[] {
   const out: FootingBar[] = [];
-  for (const b of bottomBars(Lf, Wf, Hf)) out.push({ ...b, note: '교각축' });
-  for (const b of crossBars(Lf, Wf, Hf)) out.push({ ...b, note: '교각축 직각' });
-  for (const b of sideBars(Lf, Wf, Hf)) out.push({ ...b, note: '측면 수평' });
-  for (const b of assemblyBars(Lf, Wf, Hf)) out.push({ ...b, note: '조립 수평' });
-  const b9 = shearB9(Lf, Wf, Hf, columnX);
+  for (const b of bottomBars(Lf, Wf, Hf, f)) out.push({ ...b, note: '교각축' });
+  for (const b of crossBars(Lf, Wf, Hf, f)) out.push({ ...b, note: '교각축 직각' });
+  for (const b of sideBars(Lf, Wf, Hf, f)) out.push({ ...b, note: '측면 수평' });
+  for (const b of assemblyBars(Lf, Wf, Hf, f)) out.push({ ...b, note: '조립 수평' });
+  const b9 = shearB9(Lf, Wf, Hf, columnX, 2000, f);
   out.push({ name: 'B9', size: 'H16', count: b9.count, length: b9.length, note: `전단 @500 엇갈림, ${b9.rows}행, 기둥 구역 제외 (위치·갈고리는 Q-B18·B19 규칙 적용)` });
   return out;
 }
@@ -287,7 +288,7 @@ export function rebarSummary(
     for (const f of model.footings) {
       // Columns on this footing, as x mm from the footing centre (for the B9 column-zone rule).
       const columnX = model.columns.filter((c) => Math.abs(c.s - f.s) <= f.length / 2).map((c) => (c.s - f.s) * 1000);
-      for (const b of footingBarList(f.length * 1000, f.width * 1000, (f.top - f.bottom) * 1000, columnX)) {
+      for (const b of footingBarList(f.length * 1000, f.width * 1000, (f.top - f.bottom) * 1000, columnX, model.footingRebar)) {
         const cur = agg.get(b.name);
         if (cur) {
           cur.count += b.count;
diff --git a/src/core/types.ts b/src/core/types.ts
index b2ade85..ff8de09 100644
--- a/src/core/types.ts
+++ b/src/core/types.ts
@@ -1,5 +1,6 @@
 import type { CopingRebarSettings, TopSpliceSettings } from './rebar/coping-settings';
 import type { ColumnRebarSettings } from './rebar/column-settings';
+import type { FootingRebarSettings } from './rebar/footing-settings';
 
 export type PierType = 'T형' | '2주형' | '3주형';
 export type FoundationType = '말뚝기초' | '직접기초' | '현장타설말뚝';
@@ -83,6 +84,8 @@ export interface PierInput {
   topSplice?: Partial<TopSpliceSettings>;
   /** 기둥 배근 입력 (승인 2026-10-26, 시안 ③ 기둥). Absent = the 기둥철근 (1).md defaults. */
   columnRebar?: Partial<ColumnRebarSettings>;
+  /** 확대기초 배근 입력 (승인 2026-10-26, 시안 ③ 확대기초). Absent = the 확대기초철근 (1).md defaults. */
+  footingRebar?: Partial<FootingRebarSettings>;
   strataRows?: StrataRow[];
 }
 
diff --git a/src/main.ts b/src/main.ts
index 6aec065..ce7ee34 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -30,6 +30,8 @@ import { DEFAULT_BLOCK_REBAR, type BlockRebarSettings } from './core/rebar/beari
 import { COPING_REBAR_RANGES, copingSettingsIssues, type CopingRebarSettings, DEFAULT_COPING_REBAR, DEFAULT_TOP_SPLICE, type TopSpliceSettings } from './core/rebar/coping-settings';
 import { COLUMN_REBAR_RANGES, type ColumnRebarSettings, columnSettingsIssues, DEFAULT_COLUMN_REBAR } from './core/rebar/column-settings';
 import { columnInputFor, columnRebar } from './core/rebar/column';
+import { DEFAULT_FOOTING_REBAR, FOOTING_REBAR_RANGES, type FootingRebarSettings, footingSettingsIssues } from './core/rebar/footing-settings';
+import { legB2 } from './core/rebar/footing';
 import { columnElevationSvg } from './view/column-elevation-svg';
 import { type ColumnSection, columnSectionSvg } from './view/column-section-svg';
 import { groundSectionSvg } from './view/ground-svg';
@@ -1290,6 +1292,80 @@ function renderColumnSettings(box: HTMLDivElement, pier: Pier): void {
   box.appendChild(wrap);
 }
 
+/** 확대기초 배근 입력 (승인 2026-10-26, 시안 ③ 확대기초). Fixed rules (k = 2, Δ₂ = 100, 전단 4s · 엇갈림 2s, cycle 교대) are shown, not edited. */
+const FOOTING_REBAR_FIELDS: { key: keyof FootingRebarSettings; label: string }[] = [
+  { key: 'cTop', label: '상면 피복 (철근 중심, mm)' },
+  { key: 'cSide', label: '측면 피복 (mm)' },
+  { key: 'cBottom', label: '하면 피복 (mm)' },
+  { key: 'eMin', label: '첫 철근 최소 여유 (mm)' },
+  { key: 's', label: '격자 실간격 s (mm)' },
+  { key: 'sV', label: 'B10 높이 간격 s_v (mm)' },
+  { key: 'eTop', label: 'B5 아래 최소 여유 e_top (mm)' },
+  { key: 'n', label: '조립 단 배수 n (B10 간격의 n배)' },
+];
+
+/** 적용: the values go to the draft and the model is rebuilt only when every check passes (FT01·FT02). */
+function applyFootingRebar(name: string, next: FootingRebarSettings): void {
+  const p = state.piers.find((q) => q.input.name === name);
+  if (!p) return;
+  p.draft = { ...p.draft, footingRebar: next };
+  regenerateOne(name);
+}
+
+function renderFootingSettings(box: HTMLDivElement, pier: Pier): void {
+  if (!pier.model) return;
+  const wrap = el('div', undefined, 'bearing-ref');
+  const current: FootingRebarSettings = { ...DEFAULT_FOOTING_REBAR, ...pier.draft.footingRebar };
+  wrap.appendChild(el('p', '확대기초 배근 입력 (기본값 = 확대기초철근 (1).md · 적용을 눌러야 반영)', 'lbl'));
+  const grid = el('div', undefined, 'edit-fields');
+  const inputs = new Map<keyof FootingRebarSettings, HTMLInputElement>();
+  for (const f of FOOTING_REBAR_FIELDS) {
+    const row = el('div', undefined, 'edit-row');
+    const label = el('label', f.label);
+    const input = el('input');
+    input.type = 'number';
+    input.step = 'any';
+    input.value = String(current[f.key]);
+    input.id = `footing-${f.key}`;
+    label.htmlFor = input.id;
+    inputs.set(f.key, input);
+    const [lo, hi] = FOOTING_REBAR_RANGES[f.key];
+    const changed = current[f.key] !== DEFAULT_FOOTING_REBAR[f.key] ? ' · 기본과 다름' : '';
+    row.append(label, input, el('span', `범위 ${lo}–${hi} · 기본 ${DEFAULT_FOOTING_REBAR[f.key]}${changed}`, 'muted small'));
+    grid.appendChild(row);
+  }
+  wrap.appendChild(grid);
+  // Fixed rules and derived values (읽기 전용). Derived from the current settings of the first footing.
+  const fs = current;
+  const fixed = el('div', undefined, 'muted small');
+  const H = pier.model.footings[0] ? (pier.model.footings[0].top - pier.model.footings[0].bottom) * 1000 : undefined;
+  fixed.textContent = [
+    `상면·2단 간격 = 2s (고정) ${2 * fs.s} mm`,
+    `하면 1·2단 간격 Δ₂ (고정) 100 mm`,
+    `전단 B9 간격 4s · 행 엇갈림 2s (고정) ${4 * fs.s} · ${2 * fs.s} mm`,
+    `조립 평면 간격 4s · 연직 n·s_v (자동) ${4 * fs.s} · ${fs.n * fs.sV} mm`,
+    `cycle 배치: 교대 배치 (고정)`,
+    H === undefined ? 'B2·B6 디리 (자동): 확대기초 없음' : `B2·B6 디리 (자동) z_B1 − z_B24 = ${legB2(H, fs)} mm`,
+  ].join(' · ');
+  wrap.appendChild(fixed);
+  const msg = el('p', undefined, 'muted small');
+  const apply = el('button', '적용', 'btn small');
+  apply.type = 'button';
+  apply.addEventListener('click', () => {
+    const next = { ...current };
+    for (const f of FOOTING_REBAR_FIELDS) next[f.key] = Number(inputs.get(f.key)?.value);
+    const issues = footingSettingsIssues(next);
+    if (issues.length > 0) {
+      msg.textContent = issues.map((i) => i.message).join(' · ');
+      setError('확대기초 배근 입력을 확인하세요. 값은 반영되지 않았습니다.');
+      return;
+    }
+    applyFootingRebar(pier.input.name, next);
+  });
+  wrap.append(msg, apply);
+  box.appendChild(wrap);
+}
+
 function renderCopingDrawings(box: HTMLDivElement, pier: Pier): void {
   if (!pier.model || !rebar3d) return;
   const L = pier.model.copingL;
@@ -1366,6 +1442,7 @@ function renderRebar(): void {
   if (state.rebarMember === 'coping' && rebar3d) renderCopingDrawings(box, pier);
   if (state.rebarMember === 'coping') renderCopingSettings(box, pier);
   if (state.rebarMember === 'column') renderColumnSettings(box, pier);
+  if (state.rebarMember === 'footing') renderFootingSettings(box, pier);
   const shown = rows.filter((r) => r.member === state.rebarMember);
   box.appendChild(rebarSelectBar(shown.map((r) => r.name)));
   const table = el('table', undefined, 'grid-table rebar-table');
diff --git a/src/view/rebar3d.ts b/src/view/rebar3d.ts
index c660a93..9a31fab 100644
--- a/src/view/rebar3d.ts
+++ b/src/view/rebar3d.ts
@@ -1,6 +1,6 @@
 import * as THREE from 'three';
 import type { PierModel } from '../core/geometry';
-import { assemblyEndOffset, assemblyJs, b10Levels, b9Bars, FOOTING_DEFAULTS, gridPositions, grid, layers, legLength, legOffsets, sideDepth } from '../core/rebar/footing';
+import { assemblyEndOffset, assemblyJs, b10Levels, b9Bars, gridPositions, grid, layers, legLength, legOffsets, sideDepth } from '../core/rebar/footing';
 import { bottomPiece, MAIN, topSplicePieces, widthLayout } from '../core/rebar/coping-main';
 import { C14_INSET, c14Bars, CAP, COPING_REBAR, SHEAR_LOOP_STEP, shearBars, shearBarsMulti, shearUHeight, copingSideBars, SIDE_HOOK_LEG, stairBars, undersideAt } from '../core/rebar/coping';
 import { sideRowLevels } from '../core/coping-geom';
@@ -381,11 +381,13 @@ export function buildRebar3D(m: PierModel, common: Material = DEFAULT_MATERIAL,
     const Lf = f.length;
     const Wf = f.width;
     const Hf = (f.top - f.bottom) * 1000;
-    const z = layers(Hf);
-    const gW = grid(Wf * 1000);
-    const gL = grid(Lf * 1000);
-    const posW = (j: number) => -Wf / 2 + mm(100 + gW.e + j * 125);
-    const posL = (i: number) => -Lf / 2 + mm(100 + gL.e + i * 125);
+    // 확대기초 입력 (승인 2026-10-26): the grid, covers and layer heights come from the model's footing settings.
+    const fs = m.footingRebar;
+    const z = layers(Hf, fs);
+    const gW = grid(Wf * 1000, fs);
+    const gL = grid(Lf * 1000, fs);
+    const posW = (j: number) => -Wf / 2 + mm(fs.cSide + gW.e + j * fs.s);
+    const posL = (i: number) => -Lf / 2 + mm(fs.cSide + gL.e + i * fs.s);
     const sA = -Lf / 2 + 0.1;
     const sB = Lf / 2 - 0.1;
     const nA = -Wf / 2 + 0.1;
@@ -435,7 +437,7 @@ export function buildRebar3D(m: PierModel, common: Material = DEFAULT_MATERIAL,
     const colX = m.columns.filter((c) => Math.abs(c.s - f.s) <= Lf / 2).map((c) => (c.s - f.s) * 1000);
     const yB9Bot = bottom + mm(z.B24);
     const yB9Top = bottom + mm(z.B5);
-    for (const b of b9Bars(Lf * 1000, Wf * 1000, colX).bars) {
+    for (const b of b9Bars(Lf * 1000, Wf * 1000, colX, 2000, fs).bars) {
       const x = mm(b.x);
       const n = mm(b.n);
       const tailDir = x >= 0 ? -1 : 1;
@@ -450,13 +452,13 @@ export function buildRebar3D(m: PierModel, common: Material = DEFAULT_MATERIAL,
     };
     const hookB10 = mm(hookLength('main90', NOMINAL_DIAMETER.S19)); // 296
     const hookAsm = mm(Math.round(hookLength('main90', NOMINAL_DIAMETER.S16))); // 246
-    const d1 = sideDepth(NOMINAL_DIAMETER.S29, NOMINAL_DIAMETER.S19); // B10-1 depth (mm), on the W faces
-    const d2 = sideDepth(NOMINAL_DIAMETER.S25, NOMINAL_DIAMETER.S19); // B10-2 depth (mm), on the L faces
+    const d1 = sideDepth(NOMINAL_DIAMETER.S29, NOMINAL_DIAMETER.S19, fs); // B10-1 depth (mm), on the W faces
+    const d2 = sideDepth(NOMINAL_DIAMETER.S25, NOMINAL_DIAMETER.S19, fs); // B10-2 depth (mm), on the L faces
     const sEdge = Lf / 2 - mm(d2);
     const nEdge = Wf / 2 - mm(d1);
     const dB10 = mm(NOMINAL_DIAMETER.S19);
-    for (let j = 0; j < b10Levels(Hf); j++) {
-      const zj = bottom + mm(FOOTING_DEFAULTS.cBottom + j * FOOTING_DEFAULTS.sV);
+    for (let j = 0; j < b10Levels(Hf, fs); j++) {
+      const zj = bottom + mm(fs.cBottom + j * fs.sV);
       for (const sg of [-1, 1]) {
         // B10-2: across W at the L faces; its ends turn inward along s.
         const sp = f.s + sg * sEdge;
@@ -468,13 +470,13 @@ export function buildRebar3D(m: PierModel, common: Material = DEFAULT_MATERIAL,
       }
     }
     // B11 (across W, spread along L) and B12 (along L, spread across W) at the assembly levels, 4s apart, 2s stagger per level.
-    const xsL = gridPositions(Lf * 1000);
-    const ysW = gridPositions(Wf * 1000);
+    const xsL = gridPositions(Lf * 1000, fs);
+    const ysW = gridPositions(Wf * 1000, fs);
     const dAsm = assemblyEndOffset();
     const nAsm = Wf / 2 - mm(d1 + dAsm);
     const sAsm = Lf / 2 - mm(d2 + dAsm);
-    assemblyJs(Hf).forEach((jA, k) => {
-      const zA = bottom + mm(FOOTING_DEFAULTS.cBottom + jA * FOOTING_DEFAULTS.sV);
+    assemblyJs(Hf, fs).forEach((jA, k) => {
+      const zA = bottom + mm(fs.cBottom + jA * fs.sV);
       const zB = zA + dB10;
       const i0 = k % 2 === 0 ? 0 : 2;
       for (let iL = i0; iL < xsL.length; iL += 4) {
diff --git a/tests/footing-rebar-settings.test.ts b/tests/footing-rebar-settings.test.ts
new file mode 100644
index 0000000..8eedd55
--- /dev/null
+++ b/tests/footing-rebar-settings.test.ts
@@ -0,0 +1,39 @@
+import { describe, expect, it } from 'vitest';
+import { buildPier } from '../src/core/geometry';
+import { assemblyJs, gridPositions } from '../src/core/rebar/footing';
+import { DEFAULT_FOOTING_REBAR, FOOTING_REBAR_RANGES, footingSettingsIssues } from '../src/core/rebar/footing-settings';
+import { rebarSummary } from '../src/core/rebar/summary';
+import { loadP1 } from './helpers';
+
+describe('확대기초 배근 입력 (승인 2026-10-26, 시안 ③ 확대기초)', () => {
+  it('the defaults are inside every range and raise no issue', () => {
+    expect(footingSettingsIssues(DEFAULT_FOOTING_REBAR)).toEqual([]);
+    for (const [key, [lo, hi]] of Object.entries(FOOTING_REBAR_RANGES)) {
+      const v = DEFAULT_FOOTING_REBAR[key as keyof typeof DEFAULT_FOOTING_REBAR];
+      expect(v >= lo && v <= hi, key).toBe(true);
+    }
+  });
+
+  it('a value outside its range gives FT01; a non-integer n gives FT02', () => {
+    expect(footingSettingsIssues({ ...DEFAULT_FOOTING_REBAR, cTop: 151 })).toEqual([expect.objectContaining({ code: 'FT01', key: 'cTop' })]);
+    expect(footingSettingsIssues({ ...DEFAULT_FOOTING_REBAR, n: 2.5 })).toEqual([expect.objectContaining({ code: 'FT02', key: 'n' })]);
+  });
+
+  it('the grid spacing s reaches the grid positions and the rebar table', () => {
+    const m = buildPier({ ...loadP1(), footingRebar: { s: 150 } });
+    expect(m.footingRebar.s).toBe(150);
+    const xs = gridPositions(8000, m.footingRebar);
+    expect(xs[1] - xs[0]).toBeCloseTo(150, 6);
+    const b4 = rebarSummary(m).rows.find((r) => r.name === 'B4')!;
+    const b4Default = rebarSummary(buildPier(loadP1())).rows.find((r) => r.name === 'B4')!;
+    expect(b4.count).not.toBe(b4Default.count);
+  });
+
+  it('the 조립 단 배수 n reaches the assembly levels', () => {
+    const H = 2000;
+    const base = assemblyJs(H, DEFAULT_FOOTING_REBAR);
+    const wider = assemblyJs(H, { ...DEFAULT_FOOTING_REBAR, n: 3 });
+    expect(wider.length).toBeLessThan(base.length);
+    expect(wider.every((j) => j % 3 === 0)).toBe(true);
+  });
+});
diff --git a/tests/rebar-footing.test.ts b/tests/rebar-footing.test.ts
index 8c832ba..4e49af1 100644
--- a/tests/rebar-footing.test.ts
+++ b/tests/rebar-footing.test.ts
@@ -90,6 +90,7 @@ describe('확대기초 철근 (확대기초철근 (1).md, plan C5)', () => {
 });
 
 import { assemblyHeights, assemblyJs, b10Levels, legOffsets } from '../src/core/rebar/footing';
+import { DEFAULT_FOOTING_REBAR } from '../src/core/rebar/footing-settings';
 
 describe('확대기초 배근도 재현 (확대기초철근 (1).md §13)', () => {
   it('leg offsets: B1 +25.4, B3 +22.25, B5 +28.6, B7 +23.85', () => {
@@ -119,7 +120,7 @@ describe('확대기초 배근도 재현 (확대기초철근 (1).md §13)', () =>
   });
 
   it('variables: W 8000 with s 150 → 50 grid steps, e 150, B4 26 / B2 25; W 12000 → 92 steps, e 150', () => {
-    const g = grid(8000, 150);
+    const g = grid(8000, { ...DEFAULT_FOOTING_REBAR, s: 150 });
     expect(g.n).toBe(50);
     expect(g.e).toBeCloseTo(150, 6);
     expect(grid(12000).n).toBe(92);