Cake Serving Calculator
How many servings a cake gives — by tin size and shape — and what size you need for a guest count.
Servings come from area, not diameter.
How the cake serving calculator works
Servings come from area, not diameter. A 30 cm round cake serves more than twice as many as a 20 cm one, because area goes with the square of the radius.
Portion size is the other variable and it depends on the occasion: a wedding portion is about 25 cm², a party portion 50 cm². This uses those two conventions, and shows the tin size needed for a given headcount.
Formula: servings = tin area / portion area
Worked examples
| Inputs | Servings | Note |
|---|---|---|
| A 20 cm round, two layers | 10 | about 10 party portions |
| Wedding portions | 20 | twice as many |
| A 30 cm tin | 22 | more than twice the area |
FAQFrequently asked questions
How many does a 20 cm cake serve?
About 10 standard party portions from a two-layer cake, or 20 small wedding portions.
Why does a slightly bigger tin serve so many more?
Because servings come from area, which goes with the square of the diameter. A 30 cm tin has 2.25 times the area of a 20 cm one.
What is a wedding portion?
Roughly 25 cm² — about 2.5 cm by 10 cm. A party portion is twice that.
Do layers double the servings?
Not quite. A taller cake means slimmer slices, so two layers give about 1.6 times the servings rather than 2.
How much batter do I need?
Roughly 4 mL per square centimetre of tin per layer. Fill tins about two-thirds so they have room to rise.
Where these figures come from
- US FDA — Safe Minimum Internal Temperatures — the internal temperatures the roasting calculator targets
- NIST SP 811 — Guide for the Use of the International System of Units — the exact weight and volume conversions used throughout
- UK Food Standards Agency — food safety and labelling standards
Last checked: September 2026. Baking ratios follow standard baker's percentage practice; roasting guidance follows published safe internal temperatures.