What this calculator does
Find out how to adjust a recipe when your pan isn't the size it asks for. Recipes are written for one pan, and the one in your cupboard is often different. What matters is the area of the pan's floor. Batter spread over a bigger area comes out thinner and bakes faster. The same batter in a smaller pan comes out deeper, takes longer and may overflow. Comparing the two areas tells you how much to scale the recipe, so the batter sits at the depth the recipe intended.
Enter the shape and inside size of the recipe's pan and of yours, in inches or centimeters. The calculator works out both areas and the number to multiply every ingredient by. It also shows how deep the batter would be if you left the recipe as it is, with a note on baking time.
Where it's used
Why this math matters outside the classroom:
- Swapping pans. A baker with only a 13 × 9 pan finds it holds 117 ÷ 64 = 1.83 times what an 8-inch square holds.
- Circle area in class. Students compare an 8-inch and a 10-inch round pan and find the bigger one has (10 ÷ 8)² = 1.56 times the area.
- Bakery orders. A bakery scaling a sheet-cake batter from a 9 × 13 to an 18 × 13 pan doubles every ingredient.
- Layer cakes. Two 8-inch rounds total about 100.5 square inches, a little less than one 9 × 13 pan's 117.
- Smaller households. Halving a 9 × 13 casserole into an 8-inch square works because 64 is close to half of 117.
Grade level and standards: Grade 7; Common Core State Standards for Mathematics 7.G.B.4. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
How to use it
- Choose inches or centimeters.
- Pick the shape of the recipe's pan and enter its size. For round pans, use the diameter, the distance straight across.
- Pick the shape of your pan and enter its size.
- Multiply each ingredient by the number shown (the recipe scaler can do the math for you). Or use the depth figure to decide whether the batter will fit without scaling.
What the inputs mean
- Recipe pan diameter
- Measure across the inside of the top edge, not the outside or the bottom. Pans often narrow slightly toward the bottom.
- Recipe pan length
- Rectangular pans are named length × width, for example 13 × 9 inches. A loaf pan counts as a rectangle.
- Your pan
- Bundt, tube and other shaped pans can't be compared by floor area alone. Compare them by how many cups of water they hold instead.
- Your pan diameter
- Measure straight across the inside of the top rim.
Formula and method
round pan area = π × (diameter ÷ 2)² square pan area = side² rectangular pan area = length × width scale factor = your pan's area ÷ recipe pan's area depth if unscaled = recipe pan's area ÷ your pan's area × original depth
Here π (pi) is about 3.14, and the small ² means a number times itself. The scale factor is the number you multiply each ingredient by. The amount of batter equals the floor area times the depth. To keep the same depth, the batter, and so every ingredient, must change in step with the area. A 13 × 9 pan has 117 square inches and an 8-inch square has 64. So the larger pan needs 117 ÷ 64 = 1.83 times the batter.
Round pans grow faster than their diameter suggests, because area depends on the diameter times itself. A 10-inch round holds about 1.56 times as much as an 8-inch round, not 1.25 times. The calculator assumes both pans have straight sides of similar height.
Worked example
A brownie recipe is written for an 8-inch square pan, and you want to bake it in a 13 × 9-inch pan.
- Recipe pan area = 8² = 64 in².
- Your pan area = 13 × 9 = 117 in².
- Scale factor = 117 ÷ 64 = 1.83.
- Without scaling, the batter would be 64 ÷ 117 = 0.55 times as deep.
Result: Multiply the recipe by about 1.83. For most ingredients, making 1¾ to 2 batches is close enough.
Understanding the result
A number near 1 means you can swap the pans without changing anything. For example, a 9-inch round and an 8-inch square are within 1% of each other.
When the number is awkward, round it to a handy fraction and accept a slightly thicker or thinner bake. Or round the eggs to the nearest whole egg and adjust the rest to match.
Baking time depends mostly on depth. If you scale to the same depth, the time stays close to the original. Deeper batter takes longer and may need a slightly lower temperature. Shallower batter finishes sooner. Use the recipe's test for doneness rather than the clock.
Assumptions and limitations
- Both pans have straight sides of similar height, measured on the inside.
- The batter is filled to the same depth in both pans.
- Every ingredient scales by the same amount. That works well for most cakes, brownies and bars.
- Shaped pans such as Bundt or tube pans need a volume comparison instead.
- Rounded corners on square and rectangular pans make the true area slightly smaller.
- Rising agents (like baking powder) and baking time don't always scale perfectly for very large changes. Do a test bake before an important occasion.
Frequently asked questions
Can I bake a 9 × 13 recipe in two 9-inch round pans?
Nearly. Two 9-inch rounds give about 127 square inches, against 117 for a 9 × 13. So the layers will be slightly thinner and may bake a few minutes faster.
How do I convert a round pan recipe to a square pan?
Compare areas. A 9-inch round (about 63.6 in²) and an 8-inch square (64 in²) are almost the same, so the recipe works as written. For other sizes, divide the square's area by the round's area to get the number to multiply by.
Why isn't a 10-inch pan just 25% bigger than an 8-inch pan?
Because area grows with the diameter times itself. (10 ÷ 8)² = 1.5625, so a 10-inch round holds about 56% more batter at the same depth.
Do I need to change the oven temperature?
Usually not, if you scale the recipe to keep the same depth. But say you keep the recipe and the batter ends up much deeper. Many bakers then lower the temperature by about 25 °F and bake longer. That way the middle sets before the edges overbake.
How this calculator is checked
Method: Plane area formulas (circle πr², square s², rectangle l × w); the scale factor is the ratio of base areas at equal batter depth. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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