diff --git a/src/core/rebar/column.ts b/src/core/rebar/column.ts
index 23a5f9f..abc3e6a 100644
--- a/src/core/rebar/column.ts
+++ b/src/core/rebar/column.ts
@@ -48,9 +48,9 @@ export function columnInputFor(model: PierModel, base: ColumnInput = COLUMN_P1):
   const seg = model.segments.find((g) => col.s >= g.s0 - 1e-9 && col.s <= g.s1 + 1e-9) ?? model.segments[0];
   const Hc = Math.round((model.levelBottom - model.footings[0].top) * 1000 * 10) / 10;
   const hcop = Math.round((seg.top - model.levelBottom) * 1000 * 10) / 10;
-  // C3 (상면 3단) = the lowest coping top −127 (C1 cover) −2·57.2 (layer spacing 상면 주철근 단 간격); P1: 43.170.
+  // C3 (상면 3단) = the lowest coping top −127 (C1 cover) −2·s_lay (상면 주철근 단 간격 input); P1 was 43.170 at 57.2.
   // P1 top = C3 − 100 (계산 2026-10-23), so e_P1 = step top − (C3 − 0.1) = 485 on P1.
-  const c3 = model.copingRefTop - 0.127 - 2 * 0.0572;
+  const c3 = model.copingRefTop - 0.127 - 2 * (model.copingRebar.mainLayerGap / 1000);
   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);
diff --git a/src/core/rebar/coping-main.ts b/src/core/rebar/coping-main.ts
index 5efb564..1efd6f8 100644
--- a/src/core/rebar/coping-main.ts
+++ b/src/core/rebar/coping-main.ts
@@ -1,4 +1,5 @@
 import { DEFAULT_MATERIAL, fyOf, hookLength, Material, NOMINAL_DIAMETER, spliceLength } from './common';
+import { DEFAULT_COPING_REBAR } from './coping-settings';
 
 /**
  * C1–C8 상·하면 주철근 (plan C3 continued). Source: RAG/코핑철근.md §5, 2026-10-22 최종 정리.
@@ -10,9 +11,8 @@ export const MAIN = {
   /** 기본 간격 s_m and minimum end gap g_min. */
   spacing: 125,
   endGapMin: 80,
-  /** 상면 단 간격 s_lay (EL, m) and its horizontal step (mm). */
-  layEl: 0.057,
-  layHorizontal: 57.2,
+  /** 상면 단 가로 간격 = 2d (H29, mm). Fixed; the vertical step is the 상면 주철근 단 간격 input. */
+  layHorizontal: 2 * NOMINAL_DIAMETER.H29,
   /** 90° 갈고리 l_h (mm, as in the document). */
   hook: 472,
   /** 하면 경사 구간 수평 길이 (mm, each side) and Level width. */
@@ -56,9 +56,9 @@ export function widthLayout(B: number, dSt = NOMINAL_DIAMETER.H25, dM = NOMINAL_
   };
 }
 
-/** Top-layer EL of the k-th row (k = 1, 2, 3): z_k = z_1 − (k − 1)·s_lay (m). */
-export function topRowEl(z1: number, k: number): number {
-  return Math.round((z1 - (k - 1) * MAIN.layEl) * 1000) / 1000;
+/** Top-layer EL of the k-th row (k = 1, 2, 3): z_k = z_1 − (k − 1)·s_lay (m). s_lay is the 상면 주철근 단 간격 input. */
+export function topRowEl(z1: number, k: number, layEl = DEFAULT_COPING_REBAR.mainLayerGap / 1000): number {
+  return Math.round((z1 - (k - 1) * layEl) * 1000) / 1000;
 }
 
 /** Length of one top bar on row k: path L − 2·(c + (k−1)·step), plus two 90° hooks. */
diff --git a/src/core/rebar/coping-settings.ts b/src/core/rebar/coping-settings.ts
index a4b9623..5201a1f 100644
--- a/src/core/rebar/coping-settings.ts
+++ b/src/core/rebar/coping-settings.ts
@@ -9,7 +9,7 @@ export interface CopingRebarSettings {
   mainSpacing: number;
   /** 주철근 끝단 최소 여유 (mm). */
   mainEndGap: number;
-  /** 상면 주철근 단 간격 (mm). */
+  /** 상면 주철근 단 간격 · 세로 (mm). The horizontal step is fixed at 2d (H29, 57.2 mm). */
   mainLayerGap: number;
   /** 첫 전단철근 최소 여유 (피복 다음, mm). */
   firstShearGap: number;
@@ -33,7 +33,7 @@ export const DEFAULT_COPING_REBAR: CopingRebarSettings = {
   cover: 100,
   mainSpacing: 125,
   mainEndGap: 80,
-  mainLayerGap: 57.2,
+  mainLayerGap: 100,
   firstShearGap: 200,
   shearLegs: 6,
   spacingS: 250,
@@ -49,7 +49,7 @@ export const COPING_REBAR_RANGES: Record<keyof CopingRebarSettings, [number, num
   cover: [80, 150],
   mainSpacing: [100, 150],
   mainEndGap: [60, 100],
-  mainLayerGap: [50, 70],
+  mainLayerGap: [80, 120],
   firstShearGap: [100, 300],
   shearLegs: [4, 8],
   spacingS: [200, 350],
diff --git a/src/core/rebar/coping.ts b/src/core/rebar/coping.ts
index cbb6c60..ad0b858 100644
--- a/src/core/rebar/coping.ts
+++ b/src/core/rebar/coping.ts
@@ -4,6 +4,7 @@
  */
 import { DEFAULT_MATERIAL, developmentLength, fyOf, hookLength, Material, NOMINAL_DIAMETER } from './common';
 import { type CopingGeom, P1_COPING_GEOM } from '../coping-geom';
+import { DEFAULT_COPING_REBAR } from './coping-settings';
 export const COPING_REBAR = {
   /** 피복 (최외측 철근 중심까지). */
   cover: 100,
@@ -178,7 +179,7 @@ export function undersideAt(L: number, x: number, endBottom: number, levelBottom
  * Lower rows use the side rows 7, 5, 3, 1 from the bottom (k = m − 2(j − 1)): odd j at x_c ± 2000k, even j at x_c ± 1000 ± 2000k,
  * only where that side row exists (x_w ≤ x ≤ L − x_w). `sideRows` are the side rows (z m, x_w mm), ascending.
  */
-export function c14Bars(L: number, topEl: number, sideRows: { z: number; xw: number }[], under: (x: number) => number): C14Bar[] {
+export function c14Bars(L: number, topEl: number, sideRows: { z: number; xw: number }[], under: (x: number) => number, layEl = DEFAULT_COPING_REBAR.mainLayerGap / 1000): C14Bar[] {
   const leg = Math.round(hookLength('main90', NOMINAL_DIAMETER.H19)) / 1000; // 296 mm, EL m
   const xc = L / 2;
   const lo = COPING_REBAR.cover + C14_END_GAP;
@@ -186,7 +187,7 @@ export function c14Bars(L: number, topEl: number, sideRows: { z: number; xw: num
   const out: C14Bar[] = [];
   const dUpper = (NOMINAL_DIAMETER.H29 + NOMINAL_DIAMETER.H19) / 2000; // m, over C2 / C3 (H29)
   for (const k of [2, 3]) {
-    const z = topEl - 0.127 - (k - 1) * 0.057 + dUpper;
+    const z = topEl - 0.127 - (k - 1) * layEl + dUpper;
     for (let q = -10; q <= 10; q++) {
       const x = xc + q * 1000;
       if (x >= lo && x <= hi) out.push({ line: k - 1, x, z, legs: z - leg >= under(x) });
diff --git a/src/core/rebar/summary.ts b/src/core/rebar/summary.ts
index a9ee2dc..b180217 100644
--- a/src/core/rebar/summary.ts
+++ b/src/core/rebar/summary.ts
@@ -200,7 +200,7 @@ export function rebarSummary(
   rows.push({ member: 'coping', name: 'C13', size: 'H25', count: 4 * side.c13.length, length: null, pieces: sidePieces(side.c13), note: `측면, 끝면까지, 일자 (${2 * side.c13.length}) · ㄷ ${Math.round(hook)} (${2 * side.c13.length})` });
   // C14 / C15 / C16 are derived from the model (코핑철근.md §7–8); the document's 38 / 11 / 22 and 3852 / 4070 / 4069 are checked in the tests.
   const L14 = model.copingL * 1000;
-  const c14 = c14Bars(L14, model.copingRefTop, [...side.c12, ...side.c13], (x) => undersideAt(L14, x, model.endBottom, model.levelBottom, model.copingGeom.levelWidth));
+  const c14 = c14Bars(L14, model.copingRefTop, [...side.c12, ...side.c13], (x) => undersideAt(L14, x, model.endBottom, model.levelBottom, model.copingGeom.levelWidth), model.copingRebar.mainLayerGap / 1000);
   const lineCount = (line: number) => c14.filter((b) => b.line === line).length;
   const omitted = c14.filter((b) => !b.legs).length;
   rows.push({ member: 'coping', name: 'C14', size: 'H19', count: c14.length, length: c14Length(model.copingB * 1000), note: `위 2 줄 ${lineCount(1)} · ${lineCount(2)}본씩, 아래 ${[3, 4, 5, 6].map(lineCount).join(' · ')} (합 ${c14.length}) · 연직 발 생략 ${omitted}개 (하면 밖)` });
diff --git a/src/main.ts b/src/main.ts
index d581878..e199ecc 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -1079,7 +1079,7 @@ const COPING_REBAR_FIELDS: { key: keyof CopingRebarSettings; label: string }[] =
   { key: 'cover', label: '피복 (철근 중심, mm)' },
   { key: 'mainSpacing', label: '주철근 기본간격 (mm)' },
   { key: 'mainEndGap', label: '주철근 끝단 최소 여유 (mm)' },
-  { key: 'mainLayerGap', label: '상면 주철근 단 간격 (mm)' },
+  { key: 'mainLayerGap', label: '상면 주철근 단 간격 · 세로 (mm, 가로는 2d 고정)' },
   { key: 'firstShearGap', label: '첫 전단철근 최소 여유 (피복 다음, mm)' },
   { key: 'shearLegs', label: '전단철근 다리 수' },
   { key: 'spacingS', label: '전단철근 간격 · 경사 (mm)' },
diff --git a/src/view/rebar3d.ts b/src/view/rebar3d.ts
index 094f2e3..1927475 100644
--- a/src/view/rebar3d.ts
+++ b/src/view/rebar3d.ts
@@ -150,7 +150,7 @@ export function buildRebar3D(m: PierModel, common: Material = DEFAULT_MATERIAL,
     const topEl = m.copingRefTop;
     const hookTop = MAIN.hook / 1000;
     for (let k = 1; k <= 3; k++) {
-      const z = topEl - 0.127 - (k - 1) * 0.057;
+      const z = topEl - 0.127 - (k - 1) * (m.copingRebar.mainLayerGap / 1000);
       const xk = cover + ((k - 1) * MAIN.layHorizontal) / 1000;
       xs.forEach((n, j) => {
         const name = `C${k + (j % 2 === 1 ? 0 : 3)}`;
@@ -239,7 +239,7 @@ export function buildRebar3D(m: PierModel, common: Material = DEFAULT_MATERIAL,
     const c14Hook = mm(hookLength('main90', NOMINAL_DIAMETER.H19));
     const c14Na = -B / 2 + mm(C14_INSET);
     const c14Nb = B / 2 - mm(C14_INSET);
-    for (const b of c14Bars(L * 1000, topEl, [...side.c12, ...side.c13], (x) => undersideAt(L * 1000, x, m.endBottom, m.levelBottom, m.copingGeom.levelWidth))) {
+    for (const b of c14Bars(L * 1000, topEl, [...side.c12, ...side.c13], (x) => undersideAt(L * 1000, x, m.endBottom, m.levelBottom, m.copingGeom.levelWidth), m.copingRebar.mainLayerGap / 1000)) {
       const xm = mm(b.x);
       addBar('C14', 0, [xm, b.z, c14Na], [xm, b.z, c14Nb], NOMINAL_DIAMETER.H19, COLOR.coping);
       // 연직 발 below the coping underside is left out (코핑철근.md §8).
diff --git a/tests/column-model.test.ts b/tests/column-model.test.ts
index 6746eac..8ba4ffa 100644
--- a/tests/column-model.test.ts
+++ b/tests/column-model.test.ts
@@ -10,7 +10,7 @@ describe('기둥 철근 높이는 모델에서 (Hc · h_cop, 승인 2026-10-23)'
     expect(input.hcop).toBeCloseTo(2644, 0);
     const col = columnRebar(input);
     expect(col.zTop2).toBeCloseTo(14539, 0);
-    expect(col.zTop1).toBeCloseTo(14862, 0);
+    expect(col.zTop1).toBeCloseTo(14776, 0);
   });
 
   it('taper h2 = 3000: Level underside 39.411, Hc 11203, P2 top 13039 (= Level underside + l_d)', () => {
@@ -22,7 +22,7 @@ describe('기둥 철근 높이는 모델에서 (Hc · h_cop, 승인 2026-10-23)'
     const col = columnRebar(input);
     expect(col.zTop2).toBeCloseTo(13039, 0);
     // The P1 top is anchored to the step top (and C3), so it does not move with h2.
-    expect(col.zTop1).toBeCloseTo(14862, 0);
+    expect(col.zTop1).toBeCloseTo(14776, 0);
   });
 
   it('P3 and P6 end at the coping middle level: P1 e_top 1322; taper 3000 gives e_top 2072, P3 37 ties, P6 32 bars', () => {
diff --git a/tests/rebar-coping-main.test.ts b/tests/rebar-coping-main.test.ts
index 3df66f2..650bb93 100644
--- a/tests/rebar-coping-main.test.ts
+++ b/tests/rebar-coping-main.test.ts
@@ -19,10 +19,10 @@ describe('C1–C8 상·하면 주철근 (코핑철근.md §5, plan C3)', () => {
     expect(w.text).toBe('127 · 110.5 · 21@125 · 110.5 · 127');
   });
 
-  it('heights: 43.284 / 43.227 / 43.170 for the three top rows', () => {
+  it('heights: 43.284 / 43.184 / 43.084 for the three top rows (상면 단 간격 100)', () => {
     expect(topRowEl(43.284, 1)).toBe(43.284);
-    expect(topRowEl(43.284, 2)).toBe(43.227);
-    expect(topRowEl(43.284, 3)).toBe(43.17);
+    expect(topRowEl(43.284, 2)).toBe(43.184);
+    expect(topRowEl(43.284, 3)).toBe(43.084);
   });
 
   it('top bar lengths 12744 / 12629.6 / 12515.2 (path + 2 × 472 hook)', () => {
diff --git a/tests/rebar-stairs.test.ts b/tests/rebar-stairs.test.ts
index 50e8b1d..532e141 100644
--- a/tests/rebar-stairs.test.ts
+++ b/tests/rebar-stairs.test.ts
@@ -20,11 +20,11 @@ describe('C14 / C15 / C16 (코핑철근.md §7–8)', () => {
     expect(bars.length).toBe(38);
   });
 
-  it('C14 heights: upper 43.251 / 43.194, lower 42.810 / 42.310 / 41.810 / 41.310', () => {
+  it('C14 heights: upper 43.208 / 43.108, lower 42.810 / 42.310 / 41.810 / 41.310 (상면 단 간격 100)', () => {
     const bars = c14Bars(L, m.copingRefTop, rows, under);
     const z = (line: number) => bars.find((b) => b.line === line)!.z;
-    expect(z(1)).toBeCloseTo(43.251, 3);
-    expect(z(2)).toBeCloseTo(43.194, 3);
+    expect(z(1)).toBeCloseTo(43.208, 3);
+    expect(z(2)).toBeCloseTo(43.108, 3);
     expect([3, 4, 5, 6].map(z)).toEqual([42.81, 42.31, 41.81, 41.31].map((v) => expect.closeTo(v, 2)));
   });