Party Cake Calculator — What Size Cake for Your Party?

For 20 guests, order a 10-inch round cake (24 celebration slices) or a quarter sheet cake (24–30 slices). Both fit a single party-table footprint and add a 15% buffer for seconds. Expect to spend $35–$65 at a grocery bakery and $55–$90 at a custom decorator.

An 8-inch round cake yields 14 celebration slices (1×2 inch) or 10 hearty slices (2×3 inch). Celebration slicing is the party-industry standard — guests get a taste alongside other desserts. Hearty slicing is for cake-only events.

A round cake is taller (4–5 inches) and yields fewer slices for its width — best for photos, tiered cakes, and tabletop centerpieces. A sheet cake is shorter (2 inches) and yields more slices per dollar — best for large parties, office events, and outdoor celebrations.

A quarter sheet cake (9×13 inches) yields 24 celebration slices or 18 hearty slices. It's the most common cake size for kids' birthday parties of 15–25 guests because it fits a standard fridge shelf and serves a full classroom.

A grocery-store birthday cake for 20 guests runs $35–$65, a custom bakery cake $55–$95, and a 3-tier decorated cake $110–$185. Costco bakery is the budget option (~$22 for a half sheet that feeds 48). Add $10–$25 for custom toppers, photo prints, or fondant figures.

For under-5 parties, cupcakes are easier — no cutting, no plates, kids hold their own. For ages 5+, the cake-cutting ritual matters for the celebrant photo. Hybrid solution: small 6-inch cake for the candle moment + a dozen cupcakes for guests. Best of both at ~$30–$45 total.

For a grocery bakery, 2–3 days notice is enough. For a custom decorator with fondant figures or photo prints, order 7–10 days ahead. For a wedding-style tiered cake, 2–3 weeks. Most custom bakers charge a 20–30% rush fee for orders under 48 hours.