diff --git a/public/js/webgl-book-shape-lab.js b/public/js/webgl-book-shape-lab.js
index 710c2a6..29c60d1 100644
--- a/public/js/webgl-book-shape-lab.js
+++ b/public/js/webgl-book-shape-lab.js
@@ -65,6 +65,13 @@ const FAST_FLIP_DURATION = 900;
 const FAST_FLIP_COUNT = 10;
 const FAST_FLIP_OVERLAP = 5;
 const OPEN_SEAM_GAP = 0.003;
+const PAGE_COUNT_MIN = 40;
+const PAGE_COUNT_STEP = 10;
+const PAGE_WIDTH = 1.62;
+const PAGE_DEPTH = 2.24;
+const COVER_OVERHANG = 0.13;
+const COVER_SUPPORT_OVERHANG = 0.055;
+const HINGE_INSET = 0.07;
 const SUPPORT_ANGLE_STEPS = 720;
 const SUPPORT_ANGLE_CANDIDATES = Array.from({ length: SUPPORT_ANGLE_STEPS }, (_, sample) => {
     const angle = sample / SUPPORT_ANGLE_STEPS * Math.PI * 2;
@@ -75,6 +82,8 @@ const SUPPORT_ANGLE_CANDIDATES = Array.from({ length: SUPPORT_ANGLE_STEPS }, (_,
     };
 });
 
+const maximumPageCount = calculateMaximumPageCount();
+
 let readingProgress = readInitialProgress();
 let pageCount = readInitialPageCount();
 let lastLengthError = 0;
@@ -83,6 +92,7 @@ let lastBookModel = null;
 let activeSpineHalf = 0.08;
 let activeFlips = [];
 let pendingPageFlips = 0;
+pageCountInput.max = String(maximumPageCount);
 progressInput.value = readingProgress.toFixed(3);
 progressValue.value = readingProgress.toFixed(2);
 pageCountInput.value = String(pageCount);
@@ -165,7 +175,7 @@ function readInitialPageCount() {
 }
 
 function snapPageCount(value) {
-    return THREE.MathUtils.clamp(Math.round(value / 10) * 10, 40, 600);
+    return THREE.MathUtils.clamp(Math.round(value / PAGE_COUNT_STEP) * PAGE_COUNT_STEP, PAGE_COUNT_MIN, maximumPageCount);
 }
 
 function setReadingProgress(value) {
@@ -196,8 +206,8 @@ function rebuildBook() {
 
     const coverDepth = 2.30;
     const coverThickness = BOOK_PROFILE.coverThickness;
-    const pageWidth = 1.62;
-    const pageDepth = 2.24;
+    const pageWidth = PAGE_WIDTH;
+    const pageDepth = PAGE_DEPTH;
     const bundleCount = Math.max(4, Math.round(pageCount / 10));
     const spineWidth = calculateSpineWidth(bundleCount);
     const leftCount = calculateLeftBundleCount(bundleCount);
@@ -230,11 +240,9 @@ function addCoverAssembly(pageWidth, depth, thickness, spineWidth) {
 }
 
 function createCoverAssemblyGeometry(pageWidth, depth, thickness, spineWidth) {
-    const overhang = 0.13;
     const spineHalf = spineWidth * 0.5;
-    const hingeInset = 0.07;
-    const outerX = pageWidth + overhang;
-    const hingeX = spineHalf + hingeInset;
+    const outerX = spineHalf + pageWidth + COVER_OVERHANG;
+    const hingeX = spineHalf + HINGE_INSET;
     const outerTopY = BOOK_PROFILE.tableY + thickness;
     const connectionTopY = BOOK_PROFILE.raisedHingeY;
     const spineTopY = BOOK_PROFILE.tableY + thickness;
@@ -357,6 +365,27 @@ function calculateSpineWidth(bundleCount) {
     return high;
 }
 
+function calculateMaximumPageCount() {
+    let maximum = PAGE_COUNT_MIN;
+    for (let candidate = PAGE_COUNT_MIN; candidate <= 1000; candidate += PAGE_COUNT_STEP) {
+        const bundleCount = Math.max(4, Math.round(candidate / 10));
+        if (!isBundleCountReachable(bundleCount)) break;
+        maximum = candidate;
+    }
+    return maximum;
+}
+
+function isBundleCountReachable(bundleCount) {
+    const spineWidth = calculateSpineWidth(bundleCount);
+    const bundleSpacing = calculateBundleSpacing(bundleCount, spineWidth, bundleCount);
+    const topRank = bundleCount - 1;
+    const target = restingTarget(1, PAGE_WIDTH, topRank, bundleCount, bundleSpacing);
+    const anchor = spineCurvePoint(1, spineWidth);
+    const requiredDistance = Math.hypot(target.x - anchor.x, target.y - anchor.y);
+    const verticalRise = target.y - anchor.y;
+    return requiredDistance <= PAGE_WIDTH && verticalRise <= PAGE_WIDTH * 0.5;
+}
+
 function calculateBundleSpacing(bundleCount, spineWidth, leftCount) {
     const rightCount = bundleCount - leftCount;
     const stackIntervals = Math.max(0, leftCount - 1) + Math.max(0, rightCount - 1);
@@ -795,8 +824,8 @@ function upwardNormalAt(points, index) {
 function coverTopYAtX(x) {
     const ax = Math.abs(x);
     const spineHalf = currentSpineHalf();
-    const hingeX = spineHalf + 0.07;
-    const outerX = 1.62 + 0.055;
+    const hingeX = spineHalf + HINGE_INSET;
+    const outerX = spineHalf + PAGE_WIDTH + COVER_SUPPORT_OVERHANG;
     if (ax <= spineHalf) return BOOK_PROFILE.coverThickness;
     if (ax <= hingeX) {
         const t = (ax - spineHalf) / (hingeX - spineHalf);
diff --git a/public/webgl-book-shape-lab.html b/public/webgl-book-shape-lab.html
index 14a5fcd..aebb963 100644
--- a/public/webgl-book-shape-lab.html
+++ b/public/webgl-book-shape-lab.html
@@ -74,6 +74,6 @@
         <button id="fast_forward" type="button">Fast Forward</button>
         <output id="flip_count">0 / 10</output>
     </div>
-    <script type="module" src="/js/webgl-book-shape-lab.js?v=flip-sheet-dimensions-1"></script>
+    <script type="module" src="/js/webgl-book-shape-lab.js?v=max-reachable-cover-width-2"></script>
 </body>
 </html>