Free Buttercream Calculator

Buttercream needed

• Your cake
• Filling and coats
• Decorating and reserve
• Your recipe (optional)

Worked example

The calculator's starting cake, with its sample thicknesses. Your own technique may use more or less.

• One 8 in. round tier, 4 in. high, 2 cake layers
• Filling 1/4 in., crumb coat 1/16 in., finish coat 1/8 in.
• Decorating allowance 15%, reserve 10%
• Layer area: π × 4² = 50.3 sq in. Top and sides: 2 × π × 4 × 4 + π × 4² = 150.8 sq in.
• Filling: 1 gap × 50.3 × 1/4 in. = 12.6 cu in (0.9 cups).
• Crumb and finish coats: 150.8 × (1/16 + 1/8 in.) = 28.3 cu in (2.0 cups).
• Decorating allowance: 15% of the coats = 0.3 cups. Subtotal 3.1 cups.
• Reserve: 10% = 0.3 cups. Total: 3.4 cups, about 3 1/2 cups.

How the estimate works

It's a planning estimate from geometry. Buttercream varies in density and everyone frosts differently, so cups aren't converted to grams unless you enter your own recipe's weight per cup. The bottom of each tier isn't frosted, and each tier is frosted on its own top and sides. Filling covers the full layer (no inset for a dam), and both coats use the cake's own top and sides, which slightly underestimates the finish coat on very thick coats.

• Round tiers: layer area = π × radius²; top and sides = 2 × π × radius × height + π × radius².
• Square tiers: layer area = width²; top and sides = 4 × width × height + width².
• Filling = (number of cake layers − 1) × layer area × filling thickness.
• Crumb coat and finish coat = top-and-sides area × each coat's thickness (the finish goes on top of the crumb coat).
• Decorating allowance = a percentage of the two coats, for borders and piping.
• Cubic inches ÷ 14.4375 = US cups. The reserve percentage is added last, and batches = total cups ÷ your recipe's yield, rounded up.

How it compares with published guides

Wilton's chart lists about 3 1/2 cups to ice and decorate an 8 in. round, 2-layer, 4 in. high cake, and says its amounts are very general and include a buttercream coat and a simple top and bottom border. With its starting settings and no reserve, this calculator estimates 3.1 cups for the same cake, filling included (3.4 cups with the 10% reserve).

King Arthur Baking suggests about 3 1/2 to 4 cups for a 2-layer 8 in. or 9 in. round cake and 5 to 5 1/2 cups for a 3-layer cake, and recommends making a little extra.

Published charts are rules of thumb from experience, not measurements of a coat's thickness, and they don't all say whether filling is included. This calculator shows its geometry and each part separately, so you can adjust any thickness to match the way you work. For small cakes it estimates less than Wilton's chart, whose amounts include decorating.

Wilton: Cake baking and serving guide (icing amounts) · King Arthur Baking: How much frosting for a cake

Frequently asked questions

How much buttercream do I need for an 8-inch cake?

For an 8 in. round, 2-layer cake 4 in. high, this calculator's starting settings estimate about 3 1/2 cups including filling, decorating and a 10% reserve. Wilton's chart lists about 3 1/2 cups to ice and decorate that cake, and King Arthur Baking suggests 3 1/2 to 4 cups for a 2-layer 8 or 9 in. cake.

How much buttercream do I need for a tiered cake?

Estimate each tier on its own (its top, its sides and the filling between its layers) and add them up. Add each tier in the calculator from the top down and it shows each tier's share and the total.

How thick should a crumb coat and finish coat be?

It depends on your style. A crumb coat is a thin layer to trap crumbs; a finish coat is thicker for smooth sides or texture. The calculator's starting values (1/16 in. crumb, 1/8 in. finish) are samples: change them to match the way you frost.

Does a square cake need more buttercream than a round cake?

Yes. A square cake of the same width has more top and side area than a round one, so it takes more buttercream. Switch a tier between round and square to compare.

How do I convert cups of buttercream to grams?

Weigh one level cup of your own buttercream and enter its grams per cup. Buttercreams differ in density, so the calculator won't convert to grams without your figure.

How many batches of buttercream should I make?

Enter how many cups one batch of your recipe makes. The calculator divides the total, reserve included, by that yield and rounds up to whole batches.

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