Cake Portions Calculator

What to work out

Shape

Diameter or side, cm

Second side, cm

Cake height, cm

Portion, g

Dessert 100–120 g, generous 150 g, wedding 70–80 g.

Result

Portions33
Cake weight, kg4.07
Size24 cm across
Portion, g120
Height, cm10
Equivalent square, cm21.3

From size to weight and back

Works out how many portions a cake of a given size yields, and what diameter you need to feed a given number of guests.

'How big a cake for twenty people' has a simple answer: guests times portion size. What people disagree on is the portion — a wedding sliver is 70 to 80 g, a dessert portion 100 to 120, and 'so nobody leaves hungry' is closer to 150.

The reverse calculation is the more useful one. Given the weight you need, the calculator finds the diameter: a cake's weight is its base area times its height times its density, and sponge with buttercream runs about 0.9 g per cubic centimetre.

What this calculator shows

The number of portions and the weight of a cake of your dimensions
The diameter or square side needed for a given guest count
The equivalent square for a round tin and the other way round

What to keep in mind

Sponge with buttercream is taken at 0.9 g/cm³ — mousse cakes are heavier, airy sponges lighter.
The figure is the finished cake without decoration: fondant, fruit and chocolate work all sit on top of it.

FAQs

How many kilograms of cake for 20 people?

From 1.6 kg at wedding portions of 80 g to 3 kg at generous 150 g ones. The standard 120 g dessert portion puts it at 2.4 kg.

How many portions in a 24 cm cake?

About 33 at 10 cm tall with 120 g portions. A shallower cake at 7 cm gives roughly 23.

What size cake feeds 10?

At 120 g a portion you need 1.2 kg — a 13 cm round at 10 cm tall, or 15.6 cm if the cake is only 7 cm tall.

Round or square?

Square. For the same measurement across, its area is 27 percent larger, and it cuts without awkward offcuts at the edge.

Worked example

A cake for a party

Input: Round 24 cm, 10 cm tall, 120 g portions

Output: 33 portions, 4.07 kg

Note: The familiar 'home-sized' cake turns out far bigger than it looks: thirty-three portions is a reception, not a tea. Ten people are covered by a 13 cm cake at the same height.

Useful links

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Cake Portions Calculator

Result

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