How many servings are in a 20 cm round cake?

A 20 cm round cake has a top surface of about 314 square centimetres. Cut into generous party slices of about 25 square centimetres each, it makes around 12 servings. Cut into smaller wedding fingers, the same cake stretches to about 25 servings.

How do you calculate cake servings?

Work out the top surface area of the cake, then divide by the area of one slice. For a round cake the area is pi times the radius squared; for a rectangular cake it is length times width. Dividing by the serving size and rounding down gives the number of servings.

What is the difference between a party slice and a wedding slice?

A party slice is a generous everyday portion, so a cake yields fewer of them. A wedding finger is a smaller, taller slice traditionally served at weddings, so the same cake yields many more. The serving style you choose is what changes the count, not the cake.

Cake Serving Calculator

This cake serving calculator estimates how many servings you will get from a cake, so you can bake the right size for the number of guests you need to feed. It is easy to under-cater or over-cater when you are guessing, and the answer depends on both the size of the cake and how generously you cut it. You choose the cake shape, round or rectangular, enter its dimensions in centimetres, and pick a serving style. A party slice is a generous everyday portion, a wedding finger is the small, tall slice traditionally served at weddings, and a dessert slice sits in between. The calculator works out the surface area of the cake and divides it by the area of one serving to estimate the number of servings, then rounds down so you never promise more slices than the cake can give. Use it to plan a birthday, work out how many tiers a wedding needs, or check that a single sheet cake will stretch across the office. Remember that taller cakes and layered cakes can yield slightly more per slice, and that children usually take smaller portions, so treat the figure as a sensible planning estimate rather than an exact count. Adjust the serving style to match how your guests actually eat.

Cake shape

Diameter (round)

Length (rectangular)

Width (rectangular)

Serving style

Round cakes use the diameter; rectangular cakes use length and width.

servings the cake makes

Cake area314 cm²

Per serving25 cm²

Size20 cm

A 20 cm round cake gives about 314 cm² of surface, which at 25 cm² per party serving makes about 12 servings.

A planning estimate. Taller and layered cakes may yield a little more per slice, and children usually take smaller portions.

How it works

Servings come from area, not just width. The calculator finds the top surface area of the cake: for a round cake that is pi times the radius squared, and for a rectangular cake it is length times width. It then divides that area by the area of a single serving and rounds down to a whole number. The three serving styles use different footprints: a party slice is the largest, so it gives the fewest servings; a wedding finger is the smallest, so it gives the most; and a dessert slice sits in between. Because the method is based on the cut area of the top, it works for any single tier and scales naturally as you change the size. For a multi-tier cake, work out each tier separately and add the results together.

Worked example

Take a round cake 20 centimetres across. Its radius is 10 centimetres, so the surface area is pi times 10 squared, about 314 square centimetres. Cut into party slices of about 25 square centimetres each, that is 314 divided by 25, which is 12.6, rounded down to 12 servings. Switch to wedding fingers of about 12.5 square centimetres and the same cake stretches to around 25 servings, while dessert slices of 37.5 square centimetres give about 8. The shape matters too: a 30 by 20 centimetre rectangular cake has 600 square centimetres, enough for 24 party servings.

Related calculators

Cake Pricing Calculator: what to charge for a cake.
Wedding Catering Per Head Calculator: catering cost per guest.
Cooking Measurement Converter: cups, grams and millilitres.
Wedding Guest Cost Calculator: total cost per guest.
Unit Price Calculator: price per slice or unit.

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