Buttercream Calculator

A 4 inch tall, three layer 8 inch round takes about 1,190g — roughly 5.5 cups — for a standard smooth finish with filling between the layers. A crumb coat alone needs around 700g, and a piped or textured finish closer to 1,945g. For a simpler two layer 8 inch cake, budget about 4.5 cups.

Around 758g, or about 3.5 cups, for a three layer 6 inch cake with a standard smooth finish and filling. That is roughly 245g of butter and 475g of icing sugar at the classic one-to-two ratio.

For a smooth finish on a 4 inch tall, three layer cake: about 3.5 cups for a 6 inch, 5.5 cups for an 8 inch, 8 cups for a 10 inch and 11 cups for a 12 inch. Piping roughly doubles a crumb coat, so add generously if you are covering the cake in rosettes or ruffles.

American buttercream at the standard one-to-two ratio works out at roughly 70g of butter and 135g of icing sugar per cup, plus a splash of milk and vanilla. The calculator gives you the full ingredient list alongside the total, so you can shop from it directly.

About a quarter cup per cupcake for a generous swirl, so roughly 55g each. A dozen cupcakes needs around 3 cups. A flat spread finish uses closer to half that.

Yes — make about 10% more than the calculator says if you are piping, colouring separate batches, or new to smoothing. Running out mid-way means re-making a batch that will not quite match in colour or texture, which is far worse than a little left over. Spare buttercream keeps for a week in the fridge or three months frozen.

Substantially. A piped finish uses roughly two and a half times a crumb coat on the same cake, because rosettes and ruffles stand proud of the surface rather than sitting flat against it. Choose the finish in the calculator before reading the number.

Ganache sets firmer and gives sharper edges, which is why most decorators prefer it under fondant and for anything structured. Buttercream is easier to apply and better for a soft, exposed finish, but it moves more in warm weather and shows through fondant.