How much fondant covers a cake, and how wide to roll it
Rolling fondant too small is a disaster: it will not reach the board, or it tears as you stretch it. Rolling it far too big wastes money. This fondant calculator gives the weight of fondant for a round or square cake and the size to roll it to, from the cake’s width and height. It works in inches or centimetres and shows the weight in grams and in pounds and ounces.
The rolled size is the top plus the sides plus a margin, and the weight comes from the sheet’s area, its thickness and the density of fondant. You can change the thickness, the margin and the density, add a percentage for decorations, and size several identical cakes at once. A table below lists common cake sizes at your cake height. Everything runs in your browser.
How to use the Fondant Calculator
- Choose the shape and units, then enter the cake’s width and height. Measure the height of the finished cake, including filling and its coating of buttercream or ganache.
- Leave the margin at 2 inches (5 cm) for a draped sheet, and the thickness at 3 mm (about ⅛ inch), or change them to suit your method.
- Read the rolled diameter (or square side) and the weight to buy.
- Roll the fondant on a lightly dusted surface to at least that width, and lift it over the cake with a rolling pin or both hands.
Fondant Calculator features
Rolled size and weight
The sheet size to roll and the grams or pounds and ounces to buy.
Round and square cakes
Round sheets by diameter, square sheets by side.
Adjustable thickness and margin
From a thin 2 mm sheet to a thick 6 mm one, and a bigger margin for tall cakes.
Size table
Five common cake widths at your height, so you can plan tiers or compare.
How the numbers are worked out
To cover a cake, the sheet must go over the top and down both sides, so for a round cake the rolled diameter is the cake’s diameter + 2 × its height + a margin. An 8-inch cake that is 4 inches tall needs 8 + 8 = 16 inches, and the 2-inch margin makes it 18 inches. A square cake uses the same sum for the side of a square sheet; the corners can need a little more to avoid pleats, so raise the margin for sharp edges.
The area of a round sheet is π × diameter² ÷ 4, and the weight is area × thickness × density. At 18 inches, a 3 mm sheet is about 492 cm³, and rolled fondant is roughly 1.3 g per cm³, so about 640 g, or 1 lb 7 oz. Doubling the thickness doubles the weight, which is why a thick, forgiving 5 mm sheet costs two-thirds more fondant than a 3 mm sheet.
Getting a clean finish
- Prepare the cake. A firm, smooth coat of buttercream or ganache gives the fondant something to hold on to and stops it from showing bumps.
- Roll evenly. Rolling guides or spacers keep the thickness the same. Thin spots tear; thick ones look heavy and taste doughy.
- Work quickly. Fondant skins over in minutes. Keep the unused portion wrapped tightly.
- Smooth from the top down. Press the top first, then ease out pleats on the sides with the flat of your hand, and trim the base with a sharp knife.
Related baking tools
Planning what goes under the fondant? Use the buttercream quantity calculator for the crumb and outer coat, and the ganache ratio calculator for a chocolate base. To work out batter for the tins, see the cake pan converter.
Fondant Calculator FAQ
How much fondant do I need for an 8-inch cake?
For an 8-inch round cake that is 4 inches high, about 640 g (1 lb 7 oz) rolled to 18 inches across at 3 mm. A shorter cake needs less, because the sheet only has to cover the height of the sides.
What size should I roll the fondant?
Cake diameter plus twice the height plus a margin of about 2 inches (5 cm). For a 6-inch cake that is 4 inches high, roll to about 16 inches.
How thick should fondant be?
About 3 mm (⅛ inch) for covering a cake. Go to 4 or 5 mm for a very tall cake or a hot kitchen, and avoid under 2 mm, which tears easily.
Is the amount the same for a square cake?
No. A square cake has a larger sheet area than a round cake of the same width, so it needs about a quarter more fondant in this calculation.
Does the weight include trimmings?
Yes. The whole rolled sheet is counted, including the edge you cut away. You can re-roll the offcuts for decorations, bows and plaques.
Why is my answer different from a chart?
Charts assume their own height, thickness and fondant. This tool lets you change them, and the density of fondant also varies between brands, so use it as a good estimate and keep some spare.