Tool
Pan Size Converter
Swap pan sizes and shapes, scale the recipe quantity to match, and get a real bake-time adjustment based on the actual area change, never a guess.
Pan Size Converter
Original pan
New pan
Area change: 63.6 sq in β 117.0 sq in (1.84x the batter)
Suggested oven temp adjustment: -25Β°F
The new pan is meaningfully larger in area, so the same amount of batter sits shallower and will bake faster β start checking for doneness at roughly 25-35% less time than the original recipe states.
A recipe written for a 9-inch round cake pan doesn't automatically work in an 8Γ8 square pan just because both sound like a normal size β the amount of batter surface area exposed to oven heat is genuinely different between the two, and that difference changes bake time in a way most recipes don't tell you how to handle.
This tool compares the area of your original pan against a new pan (round or rectangular, any dimensions) and tells you how to scale your batter quantity and adjust your bake time and, when needed, your oven temperature β grounded in real area geometry, not a guess.
It's built for the common situation of only owning one pan size when a recipe calls for another, or wanting to bake the same batter in a different shape (a sheet cake instead of a layer cake, for instance) without ruining the texture.
How the Pan Size Converter works
For a round pan, area is calculated with the standard circle-area formula: Ο Γ radiusΒ². For a rectangular pan, it's simply length Γ width. The tool computes both your original pan's area and your new pan's area this way, then divides new Γ· original to get an area ratio.
That area ratio IS the quantity multiplier β if the new pan has 1.5Γ the area of the original, you need 1.5Γ the batter to keep the same depth, and the same ratio also drives the bake-time guidance, since a shallower layer of batter (larger-area pan, same batter volume) cooks through faster, and a deeper layer (smaller-area pan) needs longer.
Beyond a roughly 20% area change in either direction, the tool also suggests checking or lowering the oven temperature by 25Β°F β a wider, shallower pan can brown too fast on top before the center sets if the temperature isn't adjusted down, and a much smaller, deeper pan risks the same problem in reverse (a set top over a raw center) if baked too hot for its depth.
Worked example: swapping a 9-inch round pan for a 9Γ13 rectangular pan
A 9-inch round pan has an area of Ο Γ 4.5Β² β 63.6 square inches. A 9Γ13 pan has an area of 9 Γ 13 = 117 square inches. The ratio is 117 Γ· 63.6 β 1.84 β the rectangular pan has 84% more area.
That means you'd need about 1.84Γ the batter to fill the 9Γ13 pan to the same depth as the round pan β if the recipe wasn't already designed for that pan, you'd likely be looking at closer to a 1.5β2Γ recipe. Because the ratio exceeds 1.6, the tool also suggests dropping the oven temperature by 25Β°F and checking for doneness 25β35% earlier than the original recipe's stated time, since the batter now sits noticeably shallower.
Edge cases this tool handles correctly
- Similar-area pan swaps
- If the new pan's area is within about 20% of the original (say, an 8-inch round swapped for an 8Γ8 square, which are close in area), the tool reports that bake time should stay close to the original β check at the stated time regardless, since "close" area isn't identical geometry.
- Very large area jumps
- Big jumps (more than 60% smaller, or more than 60% larger) get the strongest guidance to adjust the oven temperature, not just the time β at that scale of area change, temperature alone or time alone usually isn't enough to avoid an under- or over-baked result.
- Pan depth isn't part of this calculation
- This tool compares surface area, not volume or rim height β a very shallow vs. very deep pan of the same footprint area will still behave differently in the oven in ways area math alone doesn't capture; use the guidance as a starting point, not a guarantee.
Frequently asked questions
Why does area matter more than just "bigger pan, more time"?
Because a wider pan with the same batter volume actually means a THINNER layer of batter, which bakes FASTER, not slower β the intuitive assumption that a bigger pan needs more time is backwards for area increases; it's really about layer depth, which area ratio approximates.
Is the bake-time percentage exact?
No β it's a documented rule-of-thumb range (roughly 20β40% depending on direction and magnitude of the area change), not a guarantee down to the minute. Always start checking for doneness at the adjusted estimate rather than trusting it blindly to the exact minute.
Does this work for non-cake recipes like brownies or cornbread?
Yes β the area-ratio math applies to any batter-based bake where depth affects doneness, not specifically cakes.
What if I'm swapping to a springform or bundt pan?
Bundt and tube pans have a hole in the center that reduces usable area compared to a simple round-pan formula β this tool's area math assumes a solid round or rectangular pan and will overestimate a bundt pan's true batter capacity somewhat.