Christmas Cake Calculator

This calculator scales a traditional British Christmas cake recipe based on tin area. The base recipe is for a 20cm round tin and uses the classic rich fruit cake ratio with equal weights of currants, sultanas, and raisins.

How Scaling Works

• The tin area is calculated (circular or square) and compared to the 20cm round base. A square tin holds ~25% more than a round tin of the same dimension, so square tins need more mixture
• All ingredients are multiplied by the area ratio to maintain the correct batter depth
• The baking time is an estimate only: it starts from ~4 hours for a 20cm tin (matching Delia's Classic Christmas Cake) and is adjusted by the square root of the area ratio, since larger cakes take proportionally less extra time. Always confirm the cake is done with the skewer test — a skewer pushed into the centre should come out clean

Base Recipe (20cm Round)

• 300g each currants, sultanas, raisins
• 175g butter, 175g dark brown sugar, 175g plain flour
• 3 large eggs, 50ml brandy
• 75g mixed peel, 75g glace cherries, 50g blanched almonds

Baking-time guide (rich fruit cake, low oven): 15cm ~3.5h, 20cm ~4h, 23cm ~4¾h, 28cm ~5½h. Based on Delia Online's Classic Christmas Cake and rich fruit cake scaling guidance. Bake low and slow at 150°C (130°C fan / Gas 2) — or 140°C / Gas 1 for very large tins — and double-line the tin to stop the edges over-baking.