How do I convert a round cake recipe to a square pan?

A round pan holds less batter than a square pan of the same stated size. A 20cm round is roughly equivalent to an 18cm square. Use this calculator to get the exact volume ratio and batter multiplier.

How full should I fill a cake pan?

Fill cake pans to about two-thirds (67%) full. This allows room for the cake to rise without overflowing. For sponge cakes that rise a lot, fill to 60%. For dense cakes like fruitcake, you can fill to 75%.

Does bake time change with pan size?

Yes. Deeper pans take longer to bake because heat needs to reach the centre. As a guide, add about 5 minutes per extra centimetre of depth. Wider, shallower pans bake faster. Always check with a skewer.

How do I calculate bundt pan volume?

A bundt pan has a hollow centre tube, so its volume is the outer cylinder minus the inner cylinder. This calculator assumes the inner tube is about 40% of the outer diameter, which is a reasonable average across common designs. As a real-world guide, a standard 25cm (10-inch) bundt holds roughly 2.8 litres of liquid filled to the rim (about 10-12 US cups, per King Arthur). Bakeable capacity is lower — fill a bundt only to about two-thirds to leave room for the cake to rise.

BakeCalcs

Baking Pan Conversion Calculator

Convert recipes between different pan shapes and sizes. Calculate batter adjustments and bake time changes.

Original Pan

ShapeChoose the shape of your original cake pan

Diameter

Depth

Internal depth of the cake pan, in cm

Target Pan

ShapeChoose the shape of the cake pan you want to switch to

Length

Depth

Internal depth of the cake pan, in cm

How We Calculate This

This calculator compares the volume of two baking pans and gives you a multiplier to adjust your recipe. It accounts for different shapes, sizes, and depths.

Volume formulas

Round: π × r² × depth
Square: side × side × depth
Rectangle: length × width × depth
Bundt: π × (R² - r²) × depth (inner tube assumed ~40% of diameter)

The batter multiplier is the target volume divided by the original volume. If the multiplier is 1.5, use 1.5× the original recipe quantities. Because cake batter scales by area when the depth stays the same, a square pan holds about 27% more than a round pan of the same nominal size (the 4 ÷ π area ratio) — matching the UK baker’s rule of reducing a round tin by 2cm to get the equivalent square.

The 40%-of-diameter inner-tube figure and the 5 minutes-per-cm bake-time guide are representative averages, not exact for every pan. Always confirm doneness with a skewer rather than relying on the time estimate alone.

Frequently Asked Questions

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Last updated: March 2026

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