Cake Calculator — scale recipe to a different tin
Have a recipe for a 20 cm tin but want to bake in a 26 cm tin? This calculator works out the scaling factor for all ingredients in seconds. Enter the old diameter, the new diameter and the number of layers. Works for round tins regardless of measurement unit — grams, millilitres or whole eggs.
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How we calculate the scaling factor
Area of a circle = π × r². When the diameter changes, the area ratio = (d_new / d_old)². Example: 26/20 = 1.3, squared = 1.69. The number of layers stays the same — only ingredient quantities change proportionally to the area ratio.
Example calculation
Recipe for a 20 cm tin, baking in a 26 cm tin. Scaling factor = (26 ÷ 20)² = 1.69. If the recipe calls for 200 g flour, 100 g butter and 3 eggs: flour 200 × 1.69 = 338 g, butter 169 g, eggs ≈ 5. Multiply every ingredient by 1.69.
Frequently asked questions
How do I scale a cake recipe to a different tin?
Calculate the scaling factor: (new diameter ÷ old diameter)². Then multiply every ingredient quantity by that factor.
Why do we square the diameter ratio?
Because the area of a circle grows as the square of the radius (A = π × r²). Using a linear ratio alone would make the cake too thin.
Does baking time change when I use a bigger tin?
Yes. A larger tin usually means a shallower cake, which can reduce baking time. Check 10 minutes earlier than the recipe states.
What are standard round cake tin sizes?
Popular sizes: 16 cm (≈6 slices), 18 cm (≈8), 20 cm (≈10–12), 22 cm (≈12–14), 24 cm (≈14–16), 26 cm (≈16–20).
How do I scale the number of eggs?
Multiply the egg count by the scaling factor and round to the nearest whole number. If 3 eggs × 1.69 ≈ 5, use 5 eggs.
Does the baking temperature change?
Temperature usually stays the same. If the cake is much taller (smaller tin, same batter), reduce temperature by 10 °C and extend baking time.
How do I scale a rectangular tin?
Use surface areas: factor = (new length × new width) ÷ (old length × old width). Example: 25×35 ÷ 20×30 = 875 ÷ 600 ≈ 1.46.
How many portions does a round cake yield?
For a standard 8–10 cm tall cake, allow roughly 5 cm per birthday slice. Circumference ÷ 5 gives an approximate portion count.
How much fondant or ganache do I need to cover the cake?
Calculate top area (π × r²) plus side area (π × d × h). For a 24 cm cake 10 cm tall that is roughly 1206 cm² — plan about 600–800 g of fondant.
Can I use this for cupcake or loaf tin conversions?
For loaf tins, compare the cross-section areas (length × width). For cupcakes, divide the total batter volume by the volume of one cupcake mould.
The result is indicative. Baking time and temperature may need adjustment for a significantly different tin size.