Cake Pan Size Converter
Recipe wants a 9-inch round but you only have an 8-inch square? The base area differs, which changes batter depth and bake time. The tool assumes both pans are the same height (standard ~5 cm / 2 in home pan) and scales every ingredient by the base-area ratio — e.g. 8-in square (400 cm²) ÷ 9-in round (415 cm²) = 0.96, so cut the recipe by ~4%. A 4th-root area ratio (capped at ±25%) estimates bake-time adjustment, matching the rule-of-thumb tables in King Arthur Baking and Joy of Cooking. Works across round, square and rectangular pans.
Original recipe pan
Substitute pan
Please enter a valid number
Ingredient scale
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Suggested bake-time factor
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Original pan area
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Substitute pan area
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Formula
Round area = π·(d/2)² ; square = side² ; rectangle = L·W. Ingredient scale = A_target ⁄ A_source. Bake-time factor = clamp((A_target/A_source)^0.25, 0.75, 1.25).
- · Premise: both pans share the same height (standard home cake pan ~5 cm / 2 in). If the substitute pan is markedly deeper, batter rises higher → longer bake. The tool does not auto-correct for height.
- · Reference areas: 8-in round ≈ 322 cm², 9-in round ≈ 415 cm², 8-in square ≈ 400 cm², 9-in square ≈ 529 cm², 9×13-in rectangle ≈ 759 cm². You can sanity-check the scale factor against this list.
- · The (A_target/A_source)^0.25 bake-time factor is empirical: larger base area means faster heat exchange per unit thickness, so less time per cm. The ±25 % cap reflects the practical home-oven range; extreme ratios (>4× or <0.25×) should be split into batches or converted to cupcake / sheet form.
- · Tube / Bundt / angel-food pans add a central hole that speeds heat transfer; subtract another 5–10 % bake time on top of the area-ratio adjustment when converting to one.
- · Scaling precision: stay within 0.95–1.05× and you can use the recipe verbatim. Beyond ±10 % scale every wet, dry and leavening ingredient (baking powder / soda) proportionally. Beyond ±50 %, prefer ½ or 2× the recipe — fractional egg counts at 1.45× get awkward.
- · References: King Arthur Baking "Pan Substitutions" (2019); Joy of Cooking 75th-Anniversary "Cakes" chapter; America's Test Kitchen "Cookbook of Pan Sizes" (2018); Stella Parks, *BraveTart* (2017) Ch. 1.
- · The tool scales by base area — suitable for butter cakes, sponge, chiffon and ordinary layer cakes. Panettone, madeleines, true chiffon tubes and other shape-critical recipes need their own dedicated pan; do not retrofit them with this calculator.
Frequently asked
Why scale by base area and not volume?
Mathematically equivalent (volume = area × height), but two practical reasons favour area: (1) pans are labelled by diameter or side length ("9-inch round", "8×8 square"), almost never height, so the equal-height ~5 cm assumption is what every cookbook uses; (2) pan-substitution tables in King Arthur Baking, Joy of Cooking and America's Test Kitchen are all base-area, so the result cross-checks with those references. If your substitute pan is clearly taller (an angel-food tube at 10 cm), use the tool then add 10–15 % bake time for the extra depth.
Do I have to follow the bake-time adjustment exactly?
Treat it as a starting point, not gospel. Bake time depends heavily on oven type (convection vs. conventional), real temperature accuracy (±15 °C is normal in home ovens), recipe sugar content (high-sugar browns faster), pan material (dark metal runs ~5 °C hotter than glass). Practical workflow: (1) start checking at 70 % of the suggested time; (2) toothpick test — clean = done; (3) surface is golden brown (caramelisation has started); (4) cake pulls slightly from the pan edge. Log your result; next time you use the same substitute pan you have a personal baseline.
How do I adapt a layer-cake recipe to cupcakes or a sheet pan?
Cupcakes: a standard liner holds ~75 ml; a 9-inch round batch is ~900 ml, so one 9-in round ≈ 12 cupcakes. The tool does not directly model cupcake units, but you can approximate by treating cupcakes as a single "6 cm diameter round" (πr² ≈ 28 cm²) × 12 ≈ 336 cm² total base area, then compare to your source pan. Cupcakes bake in roughly 40 % of layer-cake time (typically 18–22 min at 175 °C). Sheet pan (US half-sheet ~33×45 cm = 1,485 cm²): a layer-cake recipe will not fill it to 1.5 cm — you would get a thin sponge. Double the recipe first.
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