diff --git a/src/core/changes.ts b/src/core/changes.ts
index db83ba6..51de119 100644
--- a/src/core/changes.ts
+++ b/src/core/changes.ts
@@ -7,6 +7,9 @@ import type { PierInput } from './types';
 export const EDITABLE_FIELDS = [
   { key: 'copingWidthMm', label: '코핑 폭 B', unit: 'mm' },
   { key: 'copingLengthMm', label: '코핑 길이 L', unit: 'mm' },
+  { key: 'copingH1Mm', label: '끝단 높이 h1', unit: 'mm' },
+  { key: 'copingH2Mm', label: '테이퍼 높이 h2', unit: 'mm' },
+  { key: 'levelWidthMm', label: 'Level 폭', unit: 'mm' },
   { key: 'pileLengthMm', label: '말뚝 길이', unit: 'mm' },
 ] as const;
 
@@ -18,6 +21,9 @@ export type EditableKey = (typeof TRACKED_KEYS)[number];
 export const FIELD_LABELS: Record<EditableKey, string> = {
   copingWidthMm: '코핑 폭 B',
   copingLengthMm: '코핑 길이 L',
+  copingH1Mm: '끝단 높이 h1',
+  copingH2Mm: '테이퍼 높이 h2',
+  levelWidthMm: 'Level 폭',
   pileLengthMm: '말뚝 길이',
   pileRows: '열별 본수',
 };
diff --git a/src/core/coping-geom.ts b/src/core/coping-geom.ts
new file mode 100644
index 0000000..7455683
--- /dev/null
+++ b/src/core/coping-geom.ts
@@ -0,0 +1,24 @@
+/**
+ * Coping heights and Level width (mm) that the coping geometry and the coping rebar depend on (1단계, 승인 2026-10-23).
+ * Dependency-free so that both the model and the rebar modules can import it.
+ */
+export interface CopingGeom {
+  /** 끝단 높이 h1 (mm). */
+  h1: number;
+  /** 테이퍼 높이 h2 (mm). */
+  h2: number;
+  /** Level 폭 W_L (mm). */
+  levelWidth: number;
+}
+
+/** P1 values: 끝단 높이 1000, 테이퍼 높이 1500, Level 폭 2100. Used when the input does not give them. */
+export const P1_COPING_GEOM: CopingGeom = { h1: 1000, h2: 1500, levelWidth: 2100 };
+
+/**
+ * Side-row levels (EL m) of C12 / C13 from the Level underside: the lowest row and the row where the sloped underside breaks.
+ * P1: 40.911 + 0.377 = 41.288 and 40.911 + 1.627 = 42.538. ASSUMPTION: the side rows keep this position relative to the
+ * Level underside when h1 or h2 changes (명세 확인 필요).
+ */
+export function sideRowLevels(levelBottom: number): { zBottom: number; zBreak: number } {
+  return { zBottom: levelBottom + 0.377, zBreak: levelBottom + 1.627 };
+}
diff --git a/src/core/geometry.ts b/src/core/geometry.ts
index 9f812de..a3f21e7 100644
--- a/src/core/geometry.ts
+++ b/src/core/geometry.ts
@@ -1,6 +1,7 @@
 import { buildAxis, copingSpan, fromAxis, kinkArc, nearKink, toAxis } from './axis';
 import { layoutText, resolveRowCounts, rowLayout, type PileGeometry } from './piles';
 import type { PierInput, Row } from './types';
+import { type CopingGeom, P1_COPING_GEOM } from './coping-geom';
 
 /** Dimensions in m. Sources: intent.PR sheet (P1 rules) and spec.md §3 defaults. */
 export const DIM = {
@@ -161,6 +162,8 @@ export interface PierModel {
   mitre: Vec2 | null;
   levelBottom: number;
   endBottom: number;
+  /** Coping heights and Level width in mm, as used by the coping rebar (1단계). */
+  copingGeom: CopingGeom;
   bearings: BearingLocal[];
   blocks: BlockModel[];
   columns: ColumnModel[];
@@ -216,6 +219,10 @@ export function buildPier(input: PierInput): PierModel {
 
   const L = input.copingLengthMm / 1000;
   const B = input.copingWidthMm / 1000;
+  // Coping heights and Level width (m): inputs, with the P1 values when absent (1단계).
+  const copingH1 = (input.copingH1Mm ?? P1_COPING_GEOM.h1) / 1000;
+  const copingH2 = (input.copingH2Mm ?? P1_COPING_GEOM.h2) / 1000;
+  const levelW = (input.levelWidthMm ?? P1_COPING_GEOM.levelWidth) / 1000;
   const planHalfB = B / 2;
   const ip1v: Vec2 = { e: ip1.x, n: ip1.y };
   const ip2v: Vec2 = { e: ip2.x, n: ip2.y };
@@ -290,20 +297,20 @@ export function buildPier(input: PierInput): PierModel {
   // Columns (spec §4.5). Positions are coping coordinates; a column must stay a Level half-width away from the kink.
   const colG = columnPositions(input.type, L);
   if (kinkG !== null) {
-    const near = nearKink(axis, colG.map((g) => sStart + g), DIM.levelWidth / 2);
+    const near = nearKink(axis, colG.map((g) => sStart + g), levelW / 2);
     if (near.length) throw new Error('미실시: 꺾임점 근처(Level 반폭 이내)에 기둥이 있습니다. 기둥 위치를 확인하세요.');
   }
   const colK = colG.map((g) => (kinkG !== null && g > kinkG ? 1 : 0));
   // Coping underside: ends at (top − end height h1 = 1000), Level zone at (top − h1 − h2 taper height = 1500).
-  const levelBottom = input.copingTopEl - DIM.copingH1 - DIM.copingH2;
-  const endBottom = input.copingTopEl - DIM.copingH1;
-  const levelStart = Math.min(...colG) - DIM.levelWidth / 2;
-  const levelEnd = Math.max(...colG) + DIM.levelWidth / 2;
+  const levelBottom = input.copingTopEl - copingH1 - copingH2;
+  const endBottom = input.copingTopEl - copingH1;
+  const levelStart = Math.min(...colG) - levelW / 2;
+  const levelEnd = Math.max(...colG) + levelW / 2;
   if (levelStart < 0 || levelEnd > L) throw new Error('코핑 길이가 Level 구간보다 짧습니다.');
 
   // Underside from the right end to the left end. Between columns (2·3주형) it drops 300 below Level with 300 × 300 haunches (spec §4.5, Q3).
   const underside: [number, number][] = [[L, endBottom]];
-  const levelZones = [...colG].sort((a, b) => b - a).map((s) => [s - DIM.levelWidth / 2, s + DIM.levelWidth / 2] as const);
+  const levelZones = [...colG].sort((a, b) => b - a).map((s) => [s - levelW / 2, s + levelW / 2] as const);
   levelZones.forEach(([zoneStart, zoneEnd], k) => {
     underside.push([zoneEnd, levelBottom], [zoneStart, levelBottom]);
     const next = levelZones[k + 1];
@@ -432,6 +439,7 @@ export function buildPier(input: PierInput): PierModel {
     mitre: axis.mitre,
     levelBottom,
     endBottom,
+    copingGeom: { h1: copingH1 * 1000, h2: copingH2 * 1000, levelWidth: levelW * 1000 },
     bearings: [...frontPlaced, ...backPlaced].map((b) => ({ no: b.no, row: b.row, k: b.k, s: b.s, g: b.g, n: b.n, z: b.z })),
     blocks,
     columns,
diff --git a/src/core/rebar/coping.ts b/src/core/rebar/coping.ts
index 7a8eaf3..c0a2588 100644
--- a/src/core/rebar/coping.ts
+++ b/src/core/rebar/coping.ts
@@ -3,6 +3,7 @@
  * Positions are along the coping length from its start, in mm.
  */
 import { DEFAULT_MATERIAL, developmentLength, fyOf, hookLength, Material, NOMINAL_DIAMETER } from './common';
+import { type CopingGeom, P1_COPING_GEOM } from '../coping-geom';
 export const COPING_REBAR = {
   /** 피복 (최외측 철근 중심까지). */
   cover: 100,
@@ -40,9 +41,9 @@ export interface ShearBars {
  * C10: @300 from the column centre, out to the first position beyond the Level edge (k_max).
  * C9 / C11: @250 outward from the outermost C10, as many as fit with the end gap of at least 300.
  */
-export function shearBars(coping: number, xc = coping / 2): ShearBars {
-  const { spacingL, spacingS, levelWidth } = COPING_REBAR;
-  const kMax = Math.ceil(levelWidth / 2 / spacingL); // k_max = ceil((W_L/2)/s_L), spec §3.1
+export function shearBars(coping: number, xc = coping / 2, g: CopingGeom = P1_COPING_GEOM): ShearBars {
+  const { spacingL, spacingS } = COPING_REBAR;
+  const kMax = Math.ceil(g.levelWidth / 2 / spacingL); // k_max = ceil((W_L/2)/s_L), spec §3.1
   const c10 = Array.from({ length: 2 * kMax + 1 }, (_, i) => Math.round(xc + (i - kMax) * spacingL));
   const left = c10[0];
   const right = c10[c10.length - 1];
@@ -82,15 +83,18 @@ export const STEP_BAR_COUNTS = { C15: 11, C16: 22 } as const;
  */
 export const SHEAR_U = { x0: 300, h0: 890.9, x1: 4550, h1: 2178.8, levelH: 2300, levelEdgeFromCentre: 1050, flat: 1740 } as const;
 
-export function shearUHeight(x: number, coping: number): number {
+/**
+ * U height at x (mm): h = (h1 − 2c) + h2·min(x_s, x_L0)/x_L0, with x_L0 = L/2 − W_L/2 (코핑철근.md §4.2).
+ * Reproduces the P1 values (890.9 at x = 300, 2178.8 at x = 4550, 2300 at the Level).
+ */
+export function shearUHeight(x: number, coping: number, g: CopingGeom = P1_COPING_GEOM): number {
   const xs = Math.min(x, coping - x); // mirror to the left half
-  const slope = (SHEAR_U.h1 - SHEAR_U.h0) / (SHEAR_U.x1 - SHEAR_U.x0);
-  const h = SHEAR_U.h0 + (xs - SHEAR_U.x0) * slope;
-  return Math.min(h, SHEAR_U.levelH);
+  const xL0 = coping / 2 - g.levelWidth / 2;
+  return g.h1 - 2 * COPING_REBAR.cover + (g.h2 * Math.min(xs, xL0)) / xL0;
 }
 
-export function shearULength(x: number, coping: number): number {
-  return SHEAR_U.flat + 2 * shearUHeight(x, coping);
+export function shearULength(x: number, coping: number, g: CopingGeom = P1_COPING_GEOM): number {
+  return SHEAR_U.flat + 2 * shearUHeight(x, coping, g);
 }
 
 /** C13 sits 127 in from each end face (코핑철근.md §6.2). */
@@ -113,13 +117,13 @@ export interface SideBar {
  * C12 meets the sloped bottom at x_w = c + (z_break − z_k)·(x_L0 − c)/h2, with x_L0 = L/2 − W_L/2.
  * C13 starts at x_w = 127. Each row has two 일자 bars (side faces) and two ㄷ bars (one at each end).
  */
-export function copingSideBars(L: number, zBottom: number, zBreak: number): { c12: SideBar[]; c13: SideBar[] } {
+export function copingSideBars(L: number, zBottom: number, zBreak: number, g: CopingGeom = P1_COPING_GEOM): { c12: SideBar[]; c13: SideBar[] } {
   const c = COPING_REBAR.cover;
-  const xL0 = L / 2 - COPING_REBAR.levelWidth / 2;
+  const xL0 = L / 2 - g.levelWidth / 2;
   const bar = (z: number, xw: number): SideBar => ({ z, xw, straight: L - 2 * xw });
   const rows = sideRows(zBottom, zBreak);
   return {
-    c12: rows.c12.map((z) => bar(z, c + ((zBreak - z) * 1000 * (xL0 - c)) / COPING_REBAR.taperHeight)),
+    c12: rows.c12.map((z) => bar(z, c + ((zBreak - z) * 1000 * (xL0 - c)) / g.h2)),
     c13: rows.c13.map((z) => bar(z, SIDE_C13_END)),
   };
 }
@@ -159,8 +163,8 @@ export interface C14Bar {
 }
 
 /** Underside of the coping (EL m) at x (mm from the start), T형: sloped from each end to the Level zone, flat in the middle. */
-export function undersideAt(L: number, x: number, endBottom: number, levelBottom: number): number {
-  const xL0 = L / 2 - COPING_REBAR.levelWidth / 2;
+export function undersideAt(L: number, x: number, endBottom: number, levelBottom: number, levelWidth = P1_COPING_GEOM.levelWidth): number {
+  const xL0 = L / 2 - levelWidth / 2;
   return endBottom + (levelBottom - endBottom) * Math.min(Math.min(x, L - x) / xL0, 1);
 }
 
@@ -246,8 +250,8 @@ export function stairBars(L: number, B: number, topEl: number, m: Material = DEF
  */
 export const CAP = { flat: 1740, cover: 100 } as const;
 
-export function capLength(x: number, coping: number): number {
-  const h = shearUHeight(x, coping);
+export function capLength(x: number, coping: number, g: CopingGeom = P1_COPING_GEOM): number {
+  const h = shearUHeight(x, coping, g);
   const lCap = h - CAP.cover;
   return CAP.flat + 2 * lCap;
 }
@@ -265,8 +269,8 @@ export const PIECES_PER_POSITION = 6;
  * 전단철근 구간 표 (시안 ③ · 코핑): the segments of C9 / C10 / C11 along the coping, from the bar positions.
  * One column gives the three T형 segments; several columns add the segments between them (추천안, Q-K2).
  */
-export function shearSegments(coping: number, columns: number[] = [coping / 2]): { segment: string; from: number; to: number; spacing: number; count: number; bar: 'C9' | 'C10' | 'C11' | 'C9·C11' }[] {
-  const b = shearBarsMulti(coping, columns);
+export function shearSegments(coping: number, columns: number[] = [coping / 2], g: CopingGeom = P1_COPING_GEOM): { segment: string; from: number; to: number; spacing: number; count: number; bar: 'C9' | 'C10' | 'C11' | 'C9·C11' }[] {
+  const b = shearBarsMulti(coping, columns, g);
   const seg = (name: string, xs: number[], bar: 'C9' | 'C10' | 'C11' | 'C9·C11', spacing: number) => ({
     segment: name,
     from: Math.min(...xs),
@@ -279,7 +283,7 @@ export function shearSegments(coping: number, columns: number[] = [coping / 2]):
   const groups = columns.length > 1 ? columns.length : 1;
   for (let k = 0; k < groups; k++) {
     const xc = columns[k] ?? coping / 2;
-    out.push(seg(`Level ${k + 1}`, b.c10.filter((x) => Math.abs(x - xc) <= (COPING_REBAR.levelWidth / 2 + COPING_REBAR.spacingL * 4)).slice(0, 2 * 4 + 1), 'C10', COPING_REBAR.spacingL));
+    out.push(seg(`Level ${k + 1}`, b.c10.filter((x) => Math.abs(x - xc) <= (g.levelWidth / 2 + COPING_REBAR.spacingL * 4)).slice(0, 2 * 4 + 1), 'C10', COPING_REBAR.spacingL));
   }
   for (let k = 0; k + 1 < groups; k++) {
     const between = b.between.filter((x) => x > columns[k] && x < columns[k + 1]);
@@ -296,13 +300,13 @@ export function shearSegments(coping: number, columns: number[] = [coping / 2]):
  * Between columns: @250 in from both C10 groups, the remaining length shared evenly (추천안, Q-K2).
  * With one column this is the same as shearBars.
  */
-export function shearBarsMulti(coping: number, columns: number[]): ShearBars & { between: number[] } {
+export function shearBarsMulti(coping: number, columns: number[], g: CopingGeom = P1_COPING_GEOM): ShearBars & { between: number[] } {
   if (columns.length <= 1) {
-    const one = shearBars(coping, columns[0] ?? coping / 2);
+    const one = shearBars(coping, columns[0] ?? coping / 2, g);
     return { ...one, between: [] };
   }
-  const { spacingL, spacingS, levelWidth } = COPING_REBAR;
-  const kMax = Math.ceil(levelWidth / 2 / spacingL); // k_max = ceil((W_L/2)/s_L), spec §3.1
+  const { spacingL, spacingS } = COPING_REBAR;
+  const kMax = Math.ceil(g.levelWidth / 2 / spacingL); // k_max = ceil((W_L/2)/s_L), spec §3.1
   const groups = columns.map((xc) =>
     Array.from({ length: 2 * kMax + 1 }, (_, i) => Math.round(xc + (i - kMax) * spacingL)),
   );
diff --git a/src/core/rebar/summary.ts b/src/core/rebar/summary.ts
index c88dbb9..9185f56 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, totals } from './bearing-block';
 import { bottomPiece, topBarLength, widthLayout } 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';
 import { columnRebar, COLUMN_P1 } from './column';
 import { bottomBars, crossBars, sideBars, assemblyBars, shearB9 } from './footing';
 import { DEFAULT_MATERIAL, FckByMember, fyOf, isAssumedMaterial, Material, materialFor, splitPieces } from './common';
@@ -162,21 +163,22 @@ export function rebarSummary(
   rows.push({ member: 'coping', name: 'C8', size: 'H29', count: perRow, length: bottom.piece, note: '하면, 2조각 겹침이음' });
   const colS = model.columns.map((c) => c.s * 1000);
   const nCol = Math.max(1, colS.length);
-  const shear = nCol > 1 ? shearBarsMulti(L, colS) : { ...shearBars(L), between: [] as number[] };
+  const geom = model.copingGeom;
+  const shear = nCol > 1 ? shearBarsMulti(L, colS, geom) : { ...shearBars(L, undefined, geom), between: [] as number[] };
   const uRange = (xs: number[]) => {
-    const u = xs.map((x) => Math.round(shearULength(x, L)));
+    const u = xs.map((x) => Math.round(shearULength(x, L, geom)));
     return `${Math.min(...u)}–${Math.max(...u)}`;
   };
   const capRange = (xs: number[]) => {
-    const c = xs.map((x) => Math.round(capLength(x, L)));
+    const c = xs.map((x) => Math.round(capLength(x, L, geom)));
     return `${Math.min(...c)}–${Math.max(...c)}`;
   };
   const shearNote = (label: string, xs: number[]) =>
     `${label}, 하부 U ${uRange(xs)}, 삿갓 ${capRange(xs)} (l_cap 추천안, Q-K5), 조각 ${xs.length * PIECES_PER_POSITION}`;
   // Each position has three 폐합, each with one 하부 U and one 삿갓 (6 pieces). Pieces: U and 삿갓 lengths at each position.
   const loopPieces = (xs: number[]) => xs.flatMap((x) => [
-    { length: shearULength(x, L), count: 3 },
-    { length: capLength(x, L), count: 3 },
+    { length: shearULength(x, L, model.copingGeom), count: 3 },
+    { length: capLength(x, L, model.copingGeom), count: 3 },
   ]);
   rows.push({ member: 'coping', name: 'C9', size: 'H25', count: shear.c9.length, length: null, pieces: loopPieces(shear.c9), note: shearNote('전단 좌 @250', shear.c9) });
   rows.push({ member: 'coping', name: 'C10', size: 'H25', count: shear.c10.length, length: null, pieces: loopPieces(shear.c10), note: shearNote('전단 Level @300', shear.c10) });
@@ -188,7 +190,8 @@ export function rebarSummary(
     warnings.push({ code: 'RB-M01', message: `다주형 ${nCol}기둥: C14는 T형 기준으로 두었습니다 (기둥마다 반복 규칙 미정, Q-K11).`, target: 'coping' });
   }
   // Per row: two 일자 (side faces) and two ㄷ (one at each end), so 4 bars per row (코핑철근.md §6.2).
-  const side = copingSideBars(model.copingL * 1000, 41.288, 42.538);
+  const levels = sideRowLevels(model.levelBottom);
+  const side = copingSideBars(model.copingL * 1000, levels.zBottom, levels.zBreak, model.copingGeom);
   const hook = model.copingB * 1000 - 2 * 127 + 2 * SIDE_HOOK_LEG; // ㄷ body across the width + two legs
   const c12Range = side.c12.length ? `${Math.round(side.c12[0].straight)}–${Math.round(side.c12[side.c12.length - 1].straight)}` : '—';
   // Per bar: 2 일자 (straight) and 2 ㄷ (hook body + legs), so 4 bars per row position.
@@ -197,7 +200,7 @@ export function rebarSummary(
   rows.push({ member: 'coping', name: 'C13', size: 'H25', count: 4 * side.c13.length, length: null, pieces: sidePieces(side.c13), note: `측면, 끝면까지, 일자 (${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));
+  const c14 = c14Bars(L14, model.copingRefTop, [...side.c12, ...side.c13], (x) => undersideAt(L14, x, model.endBottom, model.levelBottom, model.copingGeom.levelWidth));
   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/core/types.ts b/src/core/types.ts
index 6b35985..144f1de 100644
--- a/src/core/types.ts
+++ b/src/core/types.ts
@@ -31,6 +31,10 @@ export interface PierInput {
   pileLengthMm: number;
   copingWidthMm: number;
   copingLengthMm: number;
+  /** 끝단 높이 h1, 테이퍼 높이 h2, Level 폭 (mm). Absent = the P1 values (1000 · 1500 · 2100). */
+  copingH1Mm?: number;
+  copingH2Mm?: number;
+  levelWidthMm?: number;
   columnCount: number;
   /** 열별 본수 (spec §4.6): one count per 열 across the footing width. Absent = the defaults. */
   pileRows?: number[];
diff --git a/src/main.ts b/src/main.ts
index 01c56af..f3eb15d 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -15,6 +15,7 @@ import { shearSegments } from './core/rebar/coping';
 import { buildRebar3D, type RebarColorMode, type RebarScene } from './view/rebar3d';
 import { DEFAULT_MATERIAL, FCK_MEMBERS, fyOf, GRADE_CHOICES, isAssumedMaterial, materialFrom, type BendFactors, type FckByMember, type FckMember, type GradeKey, type Material } from './core/rebar/common';
 import { buildQuantity, quantityRows, type Quantity, type QuantityLine } from './core/rebar/quantity';
+import { P1_COPING_GEOM } from './core/coping-geom';
 import { allVisibleChecked, setVisibleChecked, type TypeFilter } from './core/selection';
 import { choose, defaultSummary, isSelectable, SHAPE_GROUPS, UNDEFINED_REASON, type MemberId } from './core/shape-options';
 import { parseProject, SCHEMA_VERSION, serializeProject, type ProjectFile, type ProjectInfo } from './core/project';
@@ -56,7 +57,7 @@ const CRS = '국토좌표계 (x = 동, y = 북)';
 /** 시안 ② 부재 목록 (spec §5.2). `keys` are the inputs that exist today; the rest show values only. */
 const MEMBERS: { id: MemberId; label: string; keys: EditableKey[]; note: string }[] = [
   { id: 'bearing', label: '교량받침·받침블럭·솔플레이트', keys: [], note: '받침 상세(C3)는 Q16 결정 후 추가합니다. 지금은 표시만 합니다.' },
-  { id: 'coping', label: '코핑', keys: ['copingWidthMm', 'copingLengthMm'], note: '폭과 길이를 입력합니다. 계단 위치·단차선 입력은 다음 단계에서 추가합니다.' },
+  { id: 'coping', label: '코핑', keys: ['copingWidthMm', 'copingLengthMm', 'copingH1Mm', 'copingH2Mm', 'levelWidthMm'], note: '폭, 길이, 끝단 높이 h1, 테이퍼 높이 h2, Level 폭을 입력합니다. 계단 위치·단차선 입력은 다음 단계에서 추가합니다.' },
   { id: 'column', label: '기둥', keys: [], note: '기둥 지름 입력은 다음 단계에서 추가합니다. 높이와 위치는 계산값입니다.' },
   { id: 'footing', label: '확대기초 · 말뚝', keys: ['pileLengthMm'], note: '말뚝 길이를 입력합니다. 열별 본수는 다음 단계에서 추가합니다.' },
   { id: 'ground', label: '지반·지층', keys: [], note: '지반고는 입력값을 표시만 합니다. 지층 입력은 다음 단계에서 추가합니다.' },
@@ -180,7 +181,18 @@ function animate(): void {
 animate();
 
 // --- pier model ----------------------------------------------------------------
-function buildEntry(input: PierInput, checked: boolean): Pier {
+/** Fills the coping heights and Level width with the P1 values when a file or sheet does not give them (1단계). */
+function withCopingDefaults(input: PierInput): PierInput {
+  return {
+    ...input,
+    copingH1Mm: input.copingH1Mm ?? P1_COPING_GEOM.h1,
+    copingH2Mm: input.copingH2Mm ?? P1_COPING_GEOM.h2,
+    levelWidthMm: input.levelWidthMm ?? P1_COPING_GEOM.levelWidth,
+  };
+}
+
+function buildEntry(rawInput: PierInput, checked: boolean): Pier {
+  const input = withCopingDefaults(rawInput);
   const issues: Issue[] = [];
   let model: PierModel | null = null;
   if (validateInput(input, issues)) {
@@ -971,7 +983,7 @@ function renderRebar(): void {
   renderMaterial();
   // 전단철근 구간 표 (시안 ③ 코핑 탭): segments of C9 / C10 / C11 along the coping, in metres.
   if (state.rebarMember === 'coping') {
-    const seg = shearSegments(pier.model.copingL * 1000, pier.model.columns.map((c) => c.s * 1000));
+    const seg = shearSegments(pier.model.copingL * 1000, pier.model.columns.map((c) => c.s * 1000), pier.model.copingGeom);
     const st = el('table', undefined, 'grid-table rebar-table');
     const sh = el('thead');
     const shr = el('tr');
diff --git a/src/view/rebar3d.ts b/src/view/rebar3d.ts
index 6511dc3..9103bdf 100644
--- a/src/view/rebar3d.ts
+++ b/src/view/rebar3d.ts
@@ -3,6 +3,7 @@ import type { PierModel } from '../core/geometry';
 import { assemblyEndOffset, assemblyJs, b10Levels, b9Bars, FOOTING_DEFAULTS, gridPositions, grid, layers, legLength, legOffsets, sideDepth } from '../core/rebar/footing';
 import { bottomPiece, MAIN, 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';
 import { columnRebar, COLUMN_P1 } from '../core/rebar/column';
 import { barsAcross, BLOCK_REBAR } from '../core/rebar/bearing-block';
 import { blockFramePoint } from '../core/geometry';
@@ -150,8 +151,8 @@ export function buildRebar3D(m: PierModel, common: Material = DEFAULT_MATERIAL,
     }
     // Bottom bars C7 / C8 (코핑철근.md §5.2–5.3): they follow the sloped underside, 127 above it, with a vertical leg up
     // at each end to the C1 level. Each bar is two pieces spliced at the column centre (overlap l_s). The slope runs x_L0 from each end (T형).
-    const xL0 = L / 2 - COPING_REBAR.levelWidth / 2000;
-    const under = (x: number) => undersideAt(L * 1000, x * 1000, m.endBottom, m.levelBottom);
+    const xL0 = L / 2 - m.copingGeom.levelWidth / 2000;
+    const under = (x: number) => undersideAt(L * 1000, x * 1000, m.endBottom, m.levelBottom, m.copingGeom.levelWidth);
     const lap = bottomPiece(mCoping).ls / 2000;
     xs.forEach((n, j) => {
       const z = (x: number) => under(x) + 0.127;
@@ -169,7 +170,7 @@ export function buildRebar3D(m: PierModel, common: Material = DEFAULT_MATERIAL,
     });
     // Shear loops C9 / C10 / C11 and the gaps between columns: a closed U at each position.
     const colS = m.columns.map((c) => c.s * 1000);
-    const sh = colS.length > 1 ? shearBarsMulti(L * 1000, colS) : { ...shearBars(L * 1000), between: [] as number[] };
+    const sh = colS.length > 1 ? shearBarsMulti(L * 1000, colS, m.copingGeom) : { ...shearBars(L * 1000, undefined, m.copingGeom), between: [] as number[] };
     const loops: [string, number[]][] = [['C9', sh.c9], ['C10', sh.c10], ['C11', sh.c11], ['C9·C11 사이', sh.between]];
     // Each position has three 폐합 (코핑철근.md §4.1): legs at y_i = c + i·s_leg (i = 0 … 5), 폐합 i = legs i and i + 3,
     // 1740 wide. Each 폐합 is a 하부 U (base at the bottom, legs up to the top) and a 상부 삿갓 (top bar, legs down
@@ -181,7 +182,7 @@ export function buildRebar3D(m: PierModel, common: Material = DEFAULT_MATERIAL,
     for (const [name, list] of loops) {
       for (const x of list) {
         const xm = mm(x);
-        const h = shearUHeight(x, L * 1000) / 1000;
+        const h = shearUHeight(x, L * 1000, m.copingGeom) / 1000;
         const bot = top - h;
         const capBot = top - (h - CAP.cover / 1000);
         for (let i = 0; i < 3; i++) {
@@ -203,7 +204,8 @@ export function buildRebar3D(m: PierModel, common: Material = DEFAULT_MATERIAL,
     // and two ㄷ bars: a body across the width at x_w, 25.4 above the row, with legs 1525 inward along the faces.
     const sideFace = B / 2 - 0.127;
     const dSide = NOMINAL_DIAMETER.H25;
-    const side = copingSideBars(L * 1000, 41.288, 42.538);
+    const levels = sideRowLevels(m.levelBottom);
+    const side = copingSideBars(L * 1000, levels.zBottom, levels.zBreak, m.copingGeom);
     for (const [name, rows] of [['C12', side.c12], ['C13', side.c13]] as const) {
       for (const r of rows) {
         const xw = mm(r.xw);
@@ -223,7 +225,7 @@ 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))) {
+    for (const b of c14Bars(L * 1000, topEl, [...side.c12, ...side.c13], (x) => undersideAt(L * 1000, x, m.endBottom, m.levelBottom, m.copingGeom.levelWidth))) {
       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/coping-geom.test.ts b/tests/coping-geom.test.ts
new file mode 100644
index 0000000..44db75a
--- /dev/null
+++ b/tests/coping-geom.test.ts
@@ -0,0 +1,61 @@
+import { describe, expect, it } from 'vitest';
+import { buildPier } from '../src/core/geometry';
+import { P1_COPING_GEOM, sideRowLevels } from '../src/core/coping-geom';
+import { shearUHeight, shearULength } from '../src/core/rebar/coping';
+import { rebarSummary } from '../src/core/rebar/summary';
+import { buildRebar3D } from '../src/view/rebar3d';
+import { loadP1 } from './helpers';
+
+const L = 12000;
+
+describe('① 코핑 끝단 높이 h1 · 테이퍼 높이 h2 · Level 폭 (1단계, 승인 2026-10-23)', () => {
+  it('the P1 geometry reproduces the document U heights (890.9, 2178.8, Level 2300)', () => {
+    expect(shearUHeight(300, L)).toBeCloseTo(890.9, 1);
+    expect(shearUHeight(4550, L)).toBeCloseTo(2178.8, 1);
+    expect(shearUHeight(6000, L)).toBeCloseTo(2300, 6);
+  });
+
+  it('the model defaults to the P1 coping geometry and the P1 shear lengths', () => {
+    const model = buildPier(loadP1());
+    expect(model.copingGeom).toEqual(P1_COPING_GEOM);
+    expect(model.endBottom).toBeCloseTo(43.411 - 1.0, 6);
+    expect(model.levelBottom).toBeCloseTo(43.411 - 1.0 - 1.5, 6);
+  });
+
+  it('a higher end height h1 lowers the coping ends and adds the same height to every U', () => {
+    const base = buildPier(loadP1());
+    const high = buildPier({ ...loadP1(), copingH1Mm: 1200 });
+    expect(high.endBottom).toBeCloseTo(base.endBottom - 0.2, 6);
+    expect(high.levelBottom).toBeCloseTo(base.levelBottom - 0.2, 6);
+    const geomH1 = { ...P1_COPING_GEOM, h1: 1200 };
+    expect(shearUHeight(300, L, geomH1)).toBeCloseTo(shearUHeight(300, L) + 200, 6);
+    expect(shearULength(300, L, geomH1)).toBeCloseTo(shearULength(300, L) + 400, 6);
+  });
+
+  it('a taper h2 changes the Level underside and the height at the Level', () => {
+    const high = buildPier({ ...loadP1(), copingH2Mm: 1800 });
+    expect(high.levelBottom).toBeCloseTo(43.411 - 1.0 - 1.8, 6);
+    expect(shearUHeight(6000, L, { ...P1_COPING_GEOM, h2: 1800 })).toBeCloseTo(2600, 6);
+  });
+
+  it('a wider Level changes the Level zone in the model and the shear-bar Level half-width', () => {
+    const wide = buildPier({ ...loadP1(), levelWidthMm: 2500 });
+    expect(wide.copingGeom.levelWidth).toBe(2500);
+    expect(wide.levelBottom).toBeCloseTo(buildPier(loadP1()).levelBottom, 6);
+  });
+
+  it('side-row levels keep their P1 values from the Level underside (assumption, 명세 확인 필요)', () => {
+    const levels = sideRowLevels(40.911);
+    expect(levels.zBottom).toBeCloseTo(41.288, 6);
+    expect(levels.zBreak).toBeCloseTo(42.538, 6);
+  });
+
+  it('the coping rebar follows a changed geometry: the rows and the 3D build without error, the positions are unchanged', () => {
+    const base = rebarSummary(buildPier(loadP1())).rows;
+    const changed = buildPier({ ...loadP1(), copingH1Mm: 1200, copingH2Mm: 1600, levelWidthMm: 2300 });
+    const rows = rebarSummary(changed).rows;
+    expect(rows.find((r) => r.name === 'C10')!.count).toBe(base.find((r) => r.name === 'C10')!.count);
+    expect(rows.find((r) => r.name === 'C9')!.count).toBe(base.find((r) => r.name === 'C9')!.count);
+    expect(buildRebar3D(changed).byName.get('C10')!.length).toBeGreaterThan(0);
+  });
+});