Why do I need to scale by area rather than diameter?

Doubling the diameter of a round tin quadruples its area (since area = pi x radius squared). So a 20cm recipe in a 30cm tin isn't 1.5x — it's 2.25x. Scaling by area ensures the batter depth stays consistent.

Should I adjust baking time when changing tin size?

If the batter ends up shallower (larger tin), reduce baking time by 5-10 minutes. If deeper (smaller tin), increase time and consider reducing temperature by 10°C to avoid burning the outside before the centre is done.

How do I convert between round and square tins?

A round tin and a square tin of the same stated size (e.g. both 20cm) have different areas. The square is larger. Use this calculator to get the exact ratio, or as a rule of thumb, a round tin is equivalent to a square tin about 2cm smaller.

Does tin depth matter for this calculation?

This calculator scales by the base area, which is correct when both tins have the same depth. If the new tin is shallower, you may need to reduce the quantity slightly or use two tins. If deeper, the recipe should still work but may take longer to bake.

Do I need to adjust the baking time when changing tin size?

Yes. A larger tin means shallower batter, which cooks faster — reduce baking time by about 5-10 minutes. A smaller tin means deeper batter, which takes longer — increase by 5-10 minutes and consider reducing oven temperature by 10 degrees C to prevent the top from burning before the centre is cooked.

BakeCalcs

Cake Tin Size Converter

Convert cake recipe quantities between different tin sizes and shapes based on area ratios.

Original Tin

Original Shape

Diameter

New Tin

New Shape

Diameter

How We Calculate This

This calculator compares the base area of two tins and gives you a scale factor for your recipe. A larger tin has more area, so it needs more batter to fill to the same depth.

Area Formulas

Round tin: Area = π × (diameter ÷ 2)²
Square tin: Area = side × side
Rectangular tin: Area = length × width

Scale Factor

Scale factor = New tin area ÷ Original tin area
Multiply every ingredient in your recipe by this factor

Frequently Asked Questions

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Last updated: February 2026

All calculations are based on standard ratios and conversions. Results may vary with specific ingredients, equipment, and conditions.