Cake Pan Size Converter
Scale a recipe between tins by area — where an 8 to a 10 inch round is a quarter more across and 56% more cake, and a square holds exactly 4/pi more.
Matching the area keeps the batter the same depth, which is what keeps the bake time roughly right. It does not account for a tin's sloped sides, and a much deeper or shallower fill will bake differently however carefully you scaled it — check early rather than trusting the clock. Nothing is uploaded.
A tin two inches wider holds more than half again
Pans are sold by the measurement across them and used by the area inside them, and the two do not move together. An eight to a ten is 25% more across and 56.3% more area. A six to an eight is a third wider and 77.8% bigger. So a recipe poured into the next size up comes out thin, and one poured down overflows.
| Swap | More across | More area |
|---|---|---|
| 6" → 8" | 33.3% | 77.8% |
| 8" → 9" | 12.5% | 26.6% |
| 8" → 10" | 25.0% | 56.3% |
| 9" → 12" | 33.3% | 77.8% |
| 10" → 12" | 20.0% | 44.0% |
The gain is exactly the square of the diameter ratio, which is why a third wider is always 77.8% bigger whether you go six to eight or nine to twelve. It is the same square law that makes a microscope's field sixteen times smaller for a fourfold jump, and a print twice as wide four times the paper.
And a square tin holds exactly 4/π more than a round one
A square of side d has area d²; a round of diameter d has πd²/4. The ratio is 4/π and the size cancels completely — so a square tin holds 27.32% more at six inches, at eight, at ten and at twelve alike. Which means an eight-inch square recipe poured into an eight-inch round pan is over a quarter too much batter.
| Nominal size | Round | Square | Square is bigger by |
|---|---|---|---|
| 6" | 28.27 in² | 36.00 in² | 27.3240% |
| 8" | 50.27 in² | 64.00 in² | 27.3240% |
| 9" | 63.62 in² | 81.00 in² | 27.3240% |
| 10" | 78.54 in² | 100.00 in² | 27.3240% |
| 12" | 113.10 in² | 144.00 in² | 27.3240% |
Which puts the common tins in an order that is not the order of their names.
| Tin | Area | Batter at 2" deep |
|---|---|---|
| 6 inch round | 28.27 in² | 57 in³ |
| 8 inch round | 50.27 in² | 101 in³ |
| 9 inch round | 63.62 in² | 127 in³ |
| 8 inch square | 64.00 in² | 128 in³ |
| 9 by 13 | 117.00 in² | 234 in³ |
How to use
- Enter the size the recipe was written for.
- Enter the tin you actually have.
- Pick the shape of each.
- Multiply every ingredient by the factor.
Frequently asked questions
How do I scale a recipe between pan sizes?
By AREA, not by the measurement across. Divide the area of your tin by the area of the recipe tin and multiply every ingredient by that, which keeps the batter the same depth and the bake time roughly right.
Is a 10 inch tin a quarter bigger than an 8?
A quarter wider, but 56.3% bigger. Area goes as the square of the diameter, so a recipe poured into the next size up comes out thin and one poured down overflows.
How much bigger is a 9 than an 8?
A little over a quarter — 26.6% more area for 12.5% more across. That is usually enough to matter for a layer cake and not enough to change the bake time much.
Can I use a square tin instead of a round one?
Yes, with a factor. A square of the same nominal size holds exactly 4/pi more — 27.32% — so an 8 inch square recipe in an 8 inch round pan is over a quarter too much batter.
Does that shape factor change with size?
Not at all. Both areas go as the size squared, so the ratio cancels completely: 27.32% at six inches, at eight, at ten and at twelve alike. It is one number to remember for every tin you own.
What about a 9 by 13?
117 square inches, which is bigger than any round tin most people own — half again a 9 inch round. It is the reason a traybake recipe overwhelms a layer pan so comprehensively.
Will the bake time be the same?
Roughly, if the depth is the same, which is what matching the area achieves. This does not account for a tin sloped sides, and a much deeper or shallower fill will bake differently however carefully you scaled it — check early.
Does this send anything anywhere?
No. Every figure is computed in your browser, and nothing is uploaded or stored.
🔒 This tool runs entirely in your browser. Nothing you enter is uploaded, logged, or stored.