diff --git a/.claude/settings.local.json b/.claude/settings.local.json
index 7fff6c1..37163e1 100644
--- a/.claude/settings.local.json
+++ b/.claude/settings.local.json
@@ -86,7 +86,8 @@
       "Bash(git commit -m 'Feature: Add product selection when starting design from photo request *)",
       "Bash(git commit -m 'Refactor: Move start design server action to separate file *)",
       "Bash(git commit -m 'Add: Prominent '\\\\''Shop plain items'\\\\'' section to homepage *)",
-      "Bash(git commit -m 'Feature: Royal Mail shipping integration with weight-based postage *)"
+      "Bash(git commit -m 'Feature: Royal Mail shipping integration with weight-based postage *)",
+      "Bash(git commit -m 'Add: Weight field to product admin pages *)"
     ]
   }
 }
diff --git a/src/app/admin/products/[id]/edit/page.tsx b/src/app/admin/products/[id]/edit/page.tsx
index a202724..aac09a4 100644
--- a/src/app/admin/products/[id]/edit/page.tsx
+++ b/src/app/admin/products/[id]/edit/page.tsx
@@ -239,6 +239,25 @@ export default async function EditProductPage({ params }: { params: { id: string
           </p>
         </div>
 
+        <div>
+          <label htmlFor="weightKg" className="tag-label mb-2 block">
+            Weight (kg, optional)
+          </label>
+          <input
+            id="weightKg"
+            name="weightKg"
+            type="number"
+            step="0.01"
+            min={0}
+            defaultValue={row.weightGrams != null ? (row.weightGrams / 1000).toFixed(2) : ''}
+            className="w-full border border-line bg-paper px-3 py-2 text-sm"
+            placeholder="e.g. 0.25"
+          />
+          <p className="mt-1 text-xs text-muted">
+            Used for Royal Mail shipping cost calculation at checkout. Enter weight in kilograms.
+          </p>
+        </div>
+
         <div>
           <label className="tag-label mb-2 block">Front photo</label>
           {product.imageUrl && (
diff --git a/src/app/admin/products/actions.ts b/src/app/admin/products/actions.ts
index 17eef95..adb0cb2 100644
--- a/src/app/admin/products/actions.ts
+++ b/src/app/admin/products/actions.ts
@@ -96,6 +96,10 @@ export async function createProduct(formData: FormData) {
     .map((s) => s.trim())
     .filter(Boolean);
 
+  // Weight in kilograms converted to grams
+  const weightKgInput = String(formData.get('weightKg') ?? '').trim();
+  const weightGrams = weightKgInput ? Math.round(Number(weightKgInput) * 1000) : null;
+
   const imageUrl = imageFile && imageFile.size > 0 ? await fileToDataUrl(imageFile) : null;
   const imageUrlBack = imageBackFile && imageBackFile.size > 0 ? await fileToDataUrl(imageBackFile) : null;
   const colorPhotos = await extractColorPhotos(formData, colors, 'front');
@@ -132,6 +136,7 @@ export async function createProduct(formData: FormData) {
       description: description || `${name} — personalize it your way.`,
       basePrice: Math.round(priceDollars * 100),
       personalisedPrice: personalisedPriceDollars ? Math.round(Number(personalisedPriceDollars) * 100) : null,
+      weightGrams,
       ...saleFields,
       colors: JSON.stringify(colors),
       colorPhotos: Object.keys(colorPhotos).length > 0 ? JSON.stringify(colorPhotos) : null,
@@ -173,6 +178,10 @@ export async function updateProduct(formData: FormData) {
   const referenceWidthCm = referenceWidthCmInput ? Number(referenceWidthCmInput) : null;
   const referenceHeightCm = referenceHeightCmInput ? Number(referenceHeightCmInput) : null;
 
+  // Weight in kilograms converted to grams
+  const weightKgInput = String(formData.get('weightKg') ?? '').trim();
+  const weightGrams = weightKgInput ? Math.round(Number(weightKgInput) * 1000) : null;
+
   if (!id) throw new Error('Missing product id.');
   if (!name || !category || !priceDollars) {
     throw new Error('Name, category, and price are required.');
@@ -234,6 +243,7 @@ export async function updateProduct(formData: FormData) {
     showOnProducts: boolean;
     referenceWidthCm: number | null;
     referenceHeightCm: number | null;
+    weightGrams: number | null;
     imageUrl?: string;
     imageUrlBack?: string;
     printArea?: string;
@@ -255,6 +265,7 @@ export async function updateProduct(formData: FormData) {
     showOnProducts,
     referenceWidthCm,
     referenceHeightCm,
+    weightGrams,
   };
 
   // Only touch the front photo/print area if a new photo was actually uploaded —
diff --git a/src/app/admin/products/new/page.tsx b/src/app/admin/products/new/page.tsx
index 72bb0ea..2929b69 100644
--- a/src/app/admin/products/new/page.tsx
+++ b/src/app/admin/products/new/page.tsx
@@ -214,6 +214,24 @@ export default async function NewProductPage() {
           </p>
         </div>
 
+        <div>
+          <label htmlFor="weightKg" className="tag-label mb-2 block">
+            Weight (kg, optional)
+          </label>
+          <input
+            id="weightKg"
+            name="weightKg"
+            type="number"
+            step="0.01"
+            min={0}
+            className="w-full border border-line bg-paper px-3 py-2 text-sm"
+            placeholder="e.g. 0.25"
+          />
+          <p className="mt-1 text-xs text-muted">
+            Used for Royal Mail shipping cost calculation at checkout. Enter weight in kilograms.
+          </p>
+        </div>
+
         <div>
           <label className="tag-label mb-2 block">Front photo (optional)</label>
           <PhotoPrintAreaField />