How much buttercream do you need to fill and cover a cake?
For an 8-inch round cake approximately 8cm tall, our chart allows around 970g of prepared buttercream: 400g for covering and 570g for three filling layers.
That estimate assumes approximately 1cm in each filling layer and a 0.5cm outer covering. A cake with one thin filling will need less, while a taller design or piped finish will need more.
For other sizes, use our free buttercream calculator or download the quantities chart.
Filling and covering quantities for round cakes
Buttercream Covering | CakeFlix Diploma
These figures refer to the weight of the prepared mixture, not the butter or icing sugar separately.
| Round cake diameter | Covering | Three filling layers | Total |
|---|---|---|---|
| 6 inches | 300g | 400g | 700g |
| 8 inches | 400g | 570g | 970g |
| 10 inches | 500g | 800g | 1,300g |
| 12 inches | 650g | 1,100g | 1,750g |
Chart assumptions: a cake approximately 8cm tall, three filling layers approximately 1cm thick, and an outer covering approximately 0.5cm thick. Decorative piping is additional.
Three filling layers means three filled spaces between four layers of cake. It does not mean three cake layers.
These are working estimates. Your recipe, spreading technique and chosen finish will affect how much you use.
How much buttercream for an 8-inch cake?
Make approximately 1kg for an 8-inch round cake matching the chart above. Allow extra for borders, swirls or other decorations.
If you only need to cover the outside, the guide allows approximately 400g for its stated height and coating thickness. This is not a universal allowance for every 8-inch cake.
Before preparing your batch, consider:
- The height and shape of your cake.
- How many filled layers you want.
- Whether you are also using jam, curd or another filling.
- Whether the outside needs a thin base coat or a thicker finish.
- How much piping you plan to add.
A tall celebration cake with generous fillings will need considerably more than a simple sandwich sponge of the same diameter.
Which recipe is this guide based on?
The original chart was developed around the quantities used with Paul Bradford’s buttercream tutorial.
Paul’s basic recipe uses 500g unsalted butter and 1kg icing sugar, giving approximately 1.5kg before additional ingredients. Scale both ingredients together to preserve the proportions.
Other recipes have different textures and densities. Swiss meringue and Italian meringue versions may not provide identical coverage by weight, so use this chart as a starting point.
Not sure which type you’re making? King Arthur Baking’s guide to buttercream and other frostings explains the differences between the main varieties.
Should you add ganache?
In his tutorial, Paul demonstrates adding ganache to give the mixture more structure. This is optional.
Our original guide suggests adding prepared ganache equivalent to 6% of the buttercream’s weight. For example, a 1kg batch would take 60g of prepared ganache.
This means finished ganache, not chocolate alone. The addition can affect
