Party Calculators
Party cake servings.
Enter your cake size and the slice you plan to cut, or your guest count. See the number of servings from round tiers or a rectangular cake, and the smallest round cake that feeds everyone. Runs in your browser; nothing is sent or stored.
Your party
Result
Fill the form and press Calculate.
Party Cake Servings Calculator: the short answer
Servings equal the cake top area divided by the area of one slice, times the share you can actually cut. A 10 inch round cake cut into 1.5 x 2 inch slices gives about 22 servings.
Worked example
A 10 inch round cake cut into 1.5 x 2 inch slices. Top area = pi x 10 x 10 / 4 = 78.54 square inches; one slice is 3 square inches, so 78.54 / 3 = 26.2 slices before waste; at 85% usable that is 22 servings. For 30 guests all eating cake you need 30 servings, so the smallest single round is sqrt(4 x 30 x 3 / 0.85 / pi) = 11.6 inches. A 12 inch round cut the same way gives 32 servings.
How it works
Servings = floor(cake top area / slice area x usable share). Round area = pi x diameter squared / 4; rectangle area = length x width. Tiers are added up. For a guest count, the servings needed = guests x share eating cake, rounded up, and the smallest single round diameter = sqrt(4 x servings x slice area / usable share / pi).
The 85% usable share is a planning assumption, not a standard. Use 100% for an ideal cut and a lower number for uneven or decorated cakes. Party slices are often cut narrower than a wedding slice, so try a smaller slice width if you want more servings from the same cake.
Sources and basis (opened 2026-10-08): Geometry and arithmetic on the numbers you enter. Slice size and the 85% usable share are user inputs and defaults, not sourced figures.
FAQ
How many servings are in a 10 inch round cake?
With 1.5 x 2 inch slices and 85% usable, about 22. With 1 x 2 inch slices it is about 33. The slice size you cut decides the count.
What size cake do I need for 30 people?
With 1.5 x 2 inch slices and 85% usable, a single round of about 11.6 inches, so a 12 inch round, covers 30 servings. The calculator shows the figure for your slice size.
Does a taller cake serve more?
No. Height does not change the number of slices, only how tall each one is.
How do tiers work?
Enter up to three round tier diameters and their servings are added. Rectangle cakes use one length and width.
Why not everyone eats cake?
Set the share of guests having cake below 100% if some will skip it. It reduces the servings needed.