Cake Size Calculator — Right Size for Your Guests

A round 8-inch (20cm) cake feeds 20 with standard party portions (a ~2in/5cm-wide slice, roughly 80g each). A square 8-inch feeds about 26 of the same party portions, because a grid cut wastes less than wedges. If you serve smaller finger-style slices (around 1in wide, as at a wedding or afternoon tea), the same 8-inch round can stretch to roughly 24.

A round 10-inch (25cm) cake serves approximately 30 guests on standard party portions (80-100g). A square 10-inch serves around 40 of the same party portions. Cutting smaller finger/wedding slices increases these counts by roughly 25-30%; cutting generous dessert slabs reduces them by 20-30%. The Portion Size input on this page changes the total cake weight estimate, not the recommended tin — drop down or up a size yourself if you prefer much smaller or larger slices.

For over 40 guests (round) or 54 guests (square) on party portions, a single tier becomes very large and awkward to bake and cut. Multi-tier cakes look impressive and are easier to manage. A 3-tier cake (6+8+10 inch round) serves about 60-65 party portions, since each tier’s servings simply add up.

Square cakes serve more per size because a grid cut is more efficient than slicing wedges — about 25-30% more portions for the same width. On equal party portions an 8-inch square serves about 26 versus 20 for round. Round cakes are more traditional for celebrations, so choose on theme as well as guest count.