diff --git a/lib/r2.ts b/lib/r2.ts
index 3b16deb..ddaafd7 100644
--- a/lib/r2.ts
+++ b/lib/r2.ts
@@ -35,10 +35,15 @@ export async function getPresignedReadUrl(key: string) {
   return getSignedUrl(s3, command, { expiresIn: 60 });
 }
 
-export async function signUrl(publicUrl: string) {
+export function keyFromPublicUrl(publicUrl: string): string | null {
   const prefix = process.env.R2_PUBLIC_URL!;
-  if (!publicUrl.startsWith(prefix)) return publicUrl;
-  const key = publicUrl.replace(prefix, "").replace(/^\//, "");
+  if (!publicUrl.startsWith(prefix)) return null;
+  return publicUrl.replace(prefix, "").replace(/^\//, "");
+}
+
+export async function signUrl(publicUrl: string) {
+  const key = keyFromPublicUrl(publicUrl);
+  if (key === null) return publicUrl;
   return getPresignedReadUrl(key);
 }
 
diff --git a/package-lock.json b/package-lock.json
index 45e1bfb..2e43f7e 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -11,6 +11,7 @@
         "@aws-sdk/client-s3": "^3.1015.0",
         "@aws-sdk/s3-request-presigner": "^3.1015.0",
         "@prisma/client": "^6.19.2",
+        "image-size": "^2.0.2",
         "next": "16.2.1",
         "prisma": "^6.19.2",
         "react": "19.2.4",
@@ -6355,6 +6356,18 @@
         "node": ">= 4"
       }
     },
+    "node_modules/image-size": {
+      "version": "2.0.2",
+      "resolved": "https://registry.npmjs.org/image-size/-/image-size-2.0.2.tgz",
+      "integrity": "sha512-IRqXKlaXwgSMAMtpNzZa1ZAe8m+Sa1770Dhk8VkSsP9LS+iHD62Zd8FQKs8fbPiagBE7BzoFX23cxFnwshpV6w==",
+      "license": "MIT",
+      "bin": {
+        "image-size": "bin/image-size.js"
+      },
+      "engines": {
+        "node": ">=16.x"
+      }
+    },
     "node_modules/import-fresh": {
       "version": "3.3.1",
       "resolved": "https://registry.npmjs.org/import-fresh/-/import-fresh-3.3.1.tgz",
diff --git a/package.json b/package.json
index 2b7b3e2..61e34c3 100644
--- a/package.json
+++ b/package.json
@@ -16,6 +16,7 @@
     "@aws-sdk/client-s3": "^3.1015.0",
     "@aws-sdk/s3-request-presigner": "^3.1015.0",
     "@prisma/client": "^6.19.2",
+    "image-size": "^2.0.2",
     "next": "16.2.1",
     "prisma": "^6.19.2",
     "react": "19.2.4",
diff --git a/prisma/migrations/20260412000000_add_page_dims/migration.sql b/prisma/migrations/20260412000000_add_page_dims/migration.sql
new file mode 100644
index 0000000..4c6dd88
--- /dev/null
+++ b/prisma/migrations/20260412000000_add_page_dims/migration.sql
@@ -0,0 +1,3 @@
+-- AlterTable
+ALTER TABLE "Page" ADD COLUMN     "height" INTEGER NOT NULL DEFAULT 0,
+ADD COLUMN     "width" INTEGER NOT NULL DEFAULT 0;
diff --git a/prisma/schema.prisma b/prisma/schema.prisma
index b2a5059..c005b40 100644
--- a/prisma/schema.prisma
+++ b/prisma/schema.prisma
@@ -36,6 +36,8 @@ model Page {
   chapterId Int
   number    Int
   imageUrl  String
+  width     Int     @default(0)
+  height    Int     @default(0)
   chapter   Chapter @relation(fields: [chapterId], references: [id])
 
   @@unique([chapterId, number])
diff --git a/scripts/backfill-page-dims.ts b/scripts/backfill-page-dims.ts
new file mode 100644
index 0000000..bdde175
--- /dev/null
+++ b/scripts/backfill-page-dims.ts
@@ -0,0 +1,89 @@
+/**
+ * Backfill `width` and `height` on Page rows by range-fetching the first
+ * 16 KB of each image from R2 and parsing its header with `image-size`.
+ *
+ * Idempotent: only targets rows where width=0 or height=0.
+ *
+ * Usage: npx tsx scripts/backfill-page-dims.ts
+ */
+import { PrismaClient } from "@prisma/client";
+import { S3Client, GetObjectCommand } from "@aws-sdk/client-s3";
+import { imageSize } from "image-size";
+import { keyFromPublicUrl } from "@/lib/r2";
+
+const prisma = new PrismaClient();
+
+const BUCKET = process.env.R2_BUCKET;
+if (!BUCKET) throw new Error("R2_BUCKET must be set");
+
+const s3 = new S3Client({
+  region: "auto",
+  endpoint: `https://${process.env.R2_ACCOUNT_ID}.r2.cloudflarestorage.com`,
+  credentials: {
+    accessKeyId: process.env.R2_ACCESS_KEY!,
+    secretAccessKey: process.env.R2_SECRET_KEY!,
+  },
+});
+
+const CONCURRENCY = 10;
+const HEADER_BYTES = 16_384;
+
+async function fetchHeader(key: string): Promise<Uint8Array> {
+  const res = await s3.send(
+    new GetObjectCommand({
+      Bucket: BUCKET,
+      Key: key,
+      Range: `bytes=0-${HEADER_BYTES - 1}`,
+    })
+  );
+  if (!res.Body) throw new Error(`No body for ${key}`);
+  return res.Body.transformToByteArray();
+}
+
+async function main() {
+  const pages = await prisma.page.findMany({
+    where: { OR: [{ width: 0 }, { height: 0 }] },
+    orderBy: { id: "asc" },
+  });
+  console.log(`Probing ${pages.length} pages with dims unset`);
+
+  let done = 0;
+  let failed = 0;
+
+  for (let i = 0; i < pages.length; i += CONCURRENCY) {
+    const batch = pages.slice(i, i + CONCURRENCY);
+    await Promise.all(
+      batch.map(async (page) => {
+        try {
+          const key = keyFromPublicUrl(page.imageUrl);
+          if (!key) throw new Error(`URL outside R2 prefix: ${page.imageUrl}`);
+          const header = await fetchHeader(key);
+          const { width, height } = imageSize(header);
+          if (!width || !height) {
+            throw new Error("image-size returned no dimensions");
+          }
+          await prisma.page.update({
+            where: { id: page.id },
+            data: { width, height },
+          });
+          done++;
+        } catch (err) {
+          failed++;
+          console.error(
+            `✗ page ${page.id} (${page.imageUrl}):`,
+            err instanceof Error ? err.message : err
+          );
+        }
+      })
+    );
+    console.log(`${Math.min(i + CONCURRENCY, pages.length)}/${pages.length}`);
+  }
+
+  console.log(`\nDone. Probed: ${done}, failed: ${failed}`);
+  await prisma.$disconnect();
+}
+
+main().catch((e) => {
+  console.error(e);
+  process.exit(1);
+});