Cake Serving & Tier Calculator
Servings by tin and by tier — where a 6/8/10 stack puts exactly half the cake on the bottom tier, because six squared plus eight squared is ten squared.
A wedding slice is conventionally about 1 by 2 inches and a party slice half again as wide, so the figures here are slice AREA rather than any particular cut. They assume a cake tall enough to cut in the usual way; published charts vary by an amount that is really a difference of opinion about portion size. Nothing is uploaded.
In a 6/8/10 stack the bottom tier is exactly half the cake
Servings come from area, so a tier's share is its diameter squared over the sum of the squares — and the commonest stack in the world happens to sit on a Pythagorean triple. 36 + 64 = 100, so the bottom tier is precisely as big as the two above it put together: 78.5398 square inches against 78.5398. The top two tiers are decoration and the bottom one is dinner.
| Stack | Total area | Bottom tier's share |
|---|---|---|
| 6/8/10 | 157.08 in² | 50.0000% |
| 6/9/12 | 204.99 in² | 55.1724% |
| 8/10/12 | 241.90 in² | 46.7532% |
| 4/6/8 | 91.11 in² | 55.1724% |
It is a coincidence of those sizes rather than a rule of cake, and it does not survive a change of stack — a 6/9/12 puts 55.17% on the bottom and an 8/10/12 puts 46.75%. Only the ratios matter, which is why a 4/6/8 lands on exactly the same shares as a 6/9/12.
And a ten-inch tin does not serve a quarter more than an eight
It serves 56% more — 25 slices against 39 — because the tin is a quarter wider and the square law does the rest. Working the other way, a head count implies a diameter through a square root: 20 guests want a 7.1-inch tin and 100 want 16.0, so five times the guests is barely twice the tin.
| Tin | Area | Wedding slices | Party slices |
|---|---|---|---|
| 6 inch round | 28.27 in² | 14 | 9 |
| 8 inch round | 50.27 in² | 25 | 16 |
| 9 inch round | 63.62 in² | 31 | 21 |
| 10 inch round | 78.54 in² | 39 | 26 |
| 12 inch round | 113.10 in² | 56 | 37 |
| 8 inch square | 64.00 in² | 32 | 21 |
That square root is also why big cakes get tiered rather than wide: doubling the guests costs only 41% more diameter, but a tin that feeds a hundred is already the size of an oven shelf.
| Guests | Single tin needed |
|---|---|
| 20 | 7.14" |
| 40 | 10.09" |
| 60 | 12.36" |
| 100 | 15.96" |
How to use
- Enter the tin diameter.
- Enter how many square inches a slice takes.
- Enter a guest count to work backwards.
- List your tiers to see how the servings split.
Frequently asked questions
How many does an 8 inch cake serve?
About 25 at wedding-slice size — roughly one by two inches, so two square inches each. At a more generous party slice it is nearer 16.
Does a 10 inch tin serve a quarter more than an 8?
No, over half again — 39 slices against 25. Servings come from area, and the tin is a quarter wider so the square law does the rest.
How do the tiers of a stacked cake split?
By the square of each diameter over the sum of the squares. In the standard 6/8/10 the bottom tier is exactly half the servings, because 36 plus 64 is 100 — the two upper tiers together equal the lower one.
Is that half-and-half split a rule?
No, a coincidence of those particular sizes. A 6/9/12 puts 55.17% on the bottom and an 8/10/12 puts 46.75%. Only the ratios matter, so a 4/6/8 lands on exactly the same shares as a 6/9/12.
What size tin feeds 100 people?
About 16 inches as a single tier, which is bigger than a domestic oven shelf. That is why big cakes are tiered rather than wide.
Why does the tin size grow so slowly with the guest count?
Because the diameter goes as the SQUARE ROOT of the servings. Five times the guests is only 2.24 times the tin, and doubling the guests costs just 41% more diameter.
Why do serving charts disagree with each other?
Because they disagree about portion size rather than about geometry. A chart is really telling you how big a slice its author thinks is polite, which is why the same tin is quoted anywhere from 16 to 25 servings.
Does this send anything anywhere?
No. Every figure is computed in your browser, and nothing is uploaded or stored.
🔒 This tool runs entirely in your browser. Nothing you enter is uploaded, logged, or stored.