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Divide target quantity by original quantity to get the multiplier. Scale each ingredient by this factor.
Scale factor = Target servings / Original servingsWhen scaling by pan area, compare length × width (or πr² for rounds). A 9×13 to 9×9 conversion uses area ratio, not linear dimension ratio.
Area factor = (New L × New W) / (Old L × Old W)Yeast, baking powder, salt, and leavening often scale sub-linearly. Reduce leavening slightly when doubling; increase slightly when halving. Spices may need taste adjustment rather than strict scaling.
Updated: July 2026
Scale factor 2×. Multiply flour, sugar, butter, and eggs by 2. Reduce baking powder from 2 tsp to 3.5 tsp (not 4) for best rise.
9×13 = 117 sq in; two 9" rounds = 127 sq in. Scale factor 1.09× — increase all ingredients by 9%. Adjust bake time down 5–10 minutes.
Original serves 8, target serves 2. Scale factor 0.25×. All ingredients including stock and aromatics scale linearly; check salt after tasting.
A 9-inch to 12-inch pan is not 1.33× the recipe — area increases by (12/9)² = 1.78×. Always scale by area or volume, not single dimension.
Baking powder and yeast scale sub-linearly. Double the flour but use 1.5× leavening to prevent collapse, tunneling, or bitter chemical taste.
Doubling a dinner party recipe or halving a batch of cookies should not mean recalculating every ingredient by hand. Enter original and target servings or batch sizes, and this calculator scales every ingredient proportionally while flagging items that do not scale linearly.