How many people does an 8-inch (20 cm) cake serve?

About 12 with 2-inch party slices, or 24–25 with 1 × 2 inch wedding portions. A 10-inch (25 cm) round serves about 19 party slices; a 12-inch (30 cm) about 28. Enter the size and slice width and the page counts.

How big is a cake serving?

Caterers use two standards: a party slice about 5 × 5 cm (2 × 2 in) and a wedding or dessert slice 2.5 × 5 cm (1 × 2 in), each the full height of the cake. Home slices are usually larger than either.

Does a square cake serve more than a round one of the same size?

Yes, about 27% more, because a square's area is side² while the round's is π ÷ 4 of that. A 20 cm square is 400 cm² against the 20 cm round's 314 cm².

How do I cut a round cake into equal squares?

Cut a straight line 5 cm in from one edge, then slice that strip into 5 cm pieces; repeat across the cake. The first and last strips are short and curved — that is where the rounding-down goes.

How much cake for 100 guests?

At 1 × 2 inch wedding slices, a 12-inch round gives 56, a 10-inch 39 and a 6-inch 14, so a three-tier 12 + 10 + 6 inch cake serves about 109.

Cake Servings Calculator (Round or Square, by Slice Size)

How many slices a round or square cake gives for a chosen portion size, from its dimensions.

Inputs

Shape

Diameter / side(cm)

5 cm100 cm

Height(cm)

1 cm30 cm

Slice width(cm)

2 cm15 cm

Units

Include CalculateEveryday mark

Servings

Cake volume (cm³): 2513
Per serving: 5×5 cm slice

Use this calculator on your own site

Free embed

Two lines of HTML, unlimited views
Shows a small CalculateEveryday bar, with a credit link under the calculator

What each Cake Servings input means

Shape: Round or square. Rectangular cakes work as a square of the same area.
Diameter / side: The diameter of a round cake, or the side of a square one, in cm or inches.
Height: The cake's height, used for the volume each serving holds. Standard layer cakes are about 4 inches (10 cm) tall.
Slice width: The width of each slice: about 5 cm (2 inches) for a party slice, 2.5 cm (1 inch) for a wedding finger.
Units: Metric (cm) or US units (inches). Switching converts the sizes already entered.

Cake Servings formula

round cake area = π × (diameter ÷ 2)² · square cake area = side² · servings = cake area ÷ (slice width × slice depth), rounded down

n = \left\lfloor \frac{A_{\text{cake}}}{s^{2}} \right\rfloor, \quad A_{\text{round}} = \pi \left(\frac{d}{2}\right)^{2}

The number of slices in a cake is its top area divided by the area of one slice, because slices are cut the full height. A 20 cm round has π × 10² = 314 cm² of top; cut into 5 × 5 cm portions that is 12 slices, into 2.5 × 5 cm wedding fingers 25. Height does not change the count — it changes how big each slice is — so a tall cake with the same footprint feeds the same number of people more generously, or can be cut into smaller portions. The page takes the shape, size, height and portion width, in centimetres or inches, and rounds down to whole slices; the leftover is the awkward middle piece every cake has.

Cake Servings worked example

A 20 cm round cake, 8 cm tall, cut into 5 cm party slices: the top is π × 10² = 314 cm², each slice covers 25 cm², and 314 ÷ 25 = 12.6, so 12 slices, each about 200 cm³ of cake. Cut into 2.5 cm wedding fingers it gives 25. A 20 cm square (400 cm²) gives 16 party slices, a third more than the round of the same size.

More Cake Servings examples

A 10-inch round, 4 inches tall, cut into 1-inch squares: 78.5 square inches of top gives 78 servings — enough for a dessert table where each piece is a bite.

A 30 cm square tray bake cut into 5 cm squares: 900 ÷ 25 = 36 servings.

Where the Cake Servings calculator can give the wrong answer

Rounding down is deliberate: 12.6 slices means 12 whole ones and a bit, and the bit is usually the centre or the edge that nobody gets.
Wedges from a round cake are not squares. Cutting a round cake in a grid (the caterer's method) wastes the curved edge; cutting wedges gives fewer, wider slices at the rim. The grid count is the maximum.
Tiered cakes: run each tier separately and add. Dummy tiers and decorated tops reduce the count.
Very tall cakes (over about 10 cm) are usually sliced in half horizontally by caterers, doubling the count from the same footprint; the page does not assume that.
Inch inputs are converted at 2.54 cm; a 2-inch slice is 5.08 cm, close enough to the 5 cm party portion.

Spotted a mistake? Tell us

Cake Servings reference table

Servings by cake size
Size	Round, 5 cm slices	Square, 5 cm slices	Size (US)	Round, 1 × 2 in slices	Square, 1 × 2 in slices
15 cm	7	9	6 in	14	18
20 cm	12	16	8 in	25	32
25 cm	19	25	10 in	39	50
30 cm	28	36	12 in	56	72

Source: Arithmetic: top area ÷ slice area, rounded down — π(d ÷ 2)² for a round cake, side² for a square

Cake Servings FAQ

: About 12 with 2-inch party slices, or 24–25 with 1 × 2 inch wedding portions. A 10-inch (25 cm) round serves about 19 party slices; a 12-inch (30 cm) about 28. Enter the size and slice width and the page counts.
: Caterers use two standards: a party slice about 5 × 5 cm (2 × 2 in) and a wedding or dessert slice 2.5 × 5 cm (1 × 2 in), each the full height of the cake. Home slices are usually larger than either.
: Yes, about 27% more, because a square's area is side² while the round's is π ÷ 4 of that. A 20 cm square is 400 cm² against the 20 cm round's 314 cm².
: Cut a straight line 5 cm in from one edge, then slice that strip into 5 cm pieces; repeat across the cake. The first and last strips are short and curved — that is where the rounding-down goes.
: At 1 × 2 inch wedding slices, a 12-inch round gives 56, a 10-inch 39 and a 6-inch 14, so a three-tier 12 + 10 + 6 inch cake serves about 109.