Baking Pan Size Conversion Calculator
When a recipe calls for one pan but you only have another, the safest way to convert it is by surface area rather than by the pan's name. Baked goods rise and set according to how thinly the batter is spread, which depends on area for a given amount of batter, so matching the area of the two pans keeps the depth, baking time and texture close to the original. This calculator compares a round pan and a rectangular pan: it works out the area of each, then divides the rectangular area by the round area to give a scaling factor you multiply your quantities by. A round pan's area is pi times the radius squared, and a rectangular pan's area is length times width. A 9-inch round pan covers about 63.62 square inches, while a 9 by 13 inch pan covers 117 square inches, so a recipe sized for the round would scale up by about 1.84 times. Keep the oven temperature the same and start checking for doneness a little early or late, since a thinner or deeper batter changes the timing. Every figure here is computed deterministically from the area formulas below, with a worked example that reconciles exactly to the calculator.
Scale a recipe by the ratio of pan areas: factor = new pan area / original pan area. Moving from a 9-inch round (63.62 sq in) to a 9 by 13 inch pan (117 sq in) gives a scaling factor of 1.84.
Pan area and scaling formula
round area = pi x (diameter / 2)^2
rectangular area = length x width
scaling factor = rectangular area / round area
new ingredient amount = original amount x factor
Matching area keeps the batter at a similar depth in either pan, so the bake behaves similarly. Multiply each ingredient by the scaling factor.
Worked example
Converting a recipe from a 9-inch round pan to a 9 by 13 inch rectangular pan.
- Round area: pi x (9 / 2)^2 = pi x 20.25 = 63.62 sq in.
- Rectangular area: 13 x 9 = 117 sq in.
- Scaling factor: 117 / 63.62 = 1.84.
The scaling factor is 1.84, so multiply the recipe quantities by 1.84. These are the calculator's default inputs, so the result above matches the widget exactly.
Areas of common pans
| Pan | Area (sq in) |
|---|---|
| 8-inch round | 50.27 |
| 9-inch round | 63.62 |
| 8 x 8 square | 64.00 |
| 9 x 13 rectangle | 117.00 |
Food preparation and safety guidance: US Food and Drug Administration.
Baking pan conversion calculator: frequently asked questions
How do you convert a recipe between pan sizes?
Compare the surface areas of the two pans. Divide the area of the new pan by the area of the original pan to get a scaling factor, then multiply the recipe's ingredient quantities by that factor. Matching area keeps the batter at a similar depth, which keeps baking time and texture close to the original.
How do I find a pan's area?
For a rectangular or square pan, multiply length by width. For a round pan, use pi times the radius squared, where the radius is half the diameter. For example, a 9-inch round pan has a radius of 4.5 inches and an area of about 63.62 square inches, while a 9 by 13 inch pan has an area of 117 square inches.
Why does pan area matter more than volume?
Baked goods rise and set based on how thinly the batter is spread, which depends on area for a given amount of batter. Two pans with the same area hold the batter at a similar depth, so the bake behaves similarly. Matching by area is therefore a better guide than matching the nominal pan name.
Will the baking time change?
It can. A larger area spreads the batter thinner, so it may bake faster, while a smaller area makes it deeper and slower. Keep the oven temperature the same and start checking for doneness earlier or later than the original recipe suggests, using a skewer or the spring-back test rather than the clock alone.
Should I fill a pan to the top?
No. Most cake and batter recipes fill a pan only about half to two thirds full to allow room to rise without overflowing. If a scaling factor would overfill the new pan, bake the excess separately or choose a larger pan. Following safe food handling and oven guidance from agencies such as the US Food and Drug Administration is always sensible.
Official sources
- Food preparation and safe handling guidance: US Food and Drug Administration (FDA). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.