How thick should I roll fondant?

For most cakes, roll fondant to about 5mm thick. This is thin enough to look smooth and neat but thick enough to handle without tearing. For drum or board covering, 3-4mm is fine as it does not need to drape over edges.

How do I prevent fondant from cracking?

Knead the fondant until smooth and pliable before rolling. Roll on a surface lightly dusted with icing sugar or cornflour. Work quickly to prevent it drying out, and avoid rolling it too thin. If cracks appear, smooth them with a fondant smoother and a tiny amount of vegetable fat.

Should I put buttercream under fondant?

Yes, always apply a thin, smooth coat of buttercream (or ganache) before covering with fondant. This gives the fondant something to stick to, fills any gaps or crumbs, and creates a smooth foundation that prevents the cake texture showing through.

How far in advance can I cover a cake with fondant?

A fondant-covered cake can be made 2-3 days ahead if stored in a cool, dry place. Do not refrigerate fondant-covered cakes as condensation will form and make the fondant sticky and potentially dissolve. Cover loosely with a clean cloth if needed.

How much extra fondant should I buy?

Buy about 10-15% more than calculated to account for trimming, mistakes, and any decorations. It is always better to have a little left over than to run short while covering a cake.

BakeCalcs

Fondant Coverage Calculator

Calculate how much rolled fondant you need to cover a round or square cake based on tin size and fondant thickness.

Cake ShapeWhether your cake is round or square

Cake Diameter

Cake Height

Total cake height including all layers and filling (a 2-layer cake is ≈ 9cm, 3-layer ≈ 13.5cm)

Fondant Thickness

Fondant rolling thickness; 5mm is standard for draping over edges, 3-4mm for board or drum covering

How We Calculate This

The calculator works out the total surface area of your cake (top plus sides), then multiplies by the density of rolled sugarpaste to give the covering weight in grams. Rolled fondant is essentially solid sugar paste with a density of about 1.35 g/cm³, so a layer 5mm thick weighs roughly 0.675g per cm² of cake surface.

The Formula

Round cake surface area: pi x r² (top) + 2 x pi x r x height (sides)
Square cake surface area: side² (top) + 4 x side x height (sides)
Fondant weight: surface area (cm²) x 1.35 g/cm³ x thickness (cm) — about 0.675g per cm² at 5mm
Round roll diameter: cake diameter + 2 x height + trimming allowance
Square roll diameter: diagonal (side x 1.41) + 2 x height + trimming allowance

Charts published by UK sugarpaste suppliers tend to quote slightly higher figures because they build in extra for trimming and drape, so buy about 10-15% more than the calculated weight.

Frequently Asked Questions

Related Calculators

Chocolate Tempering Calculator

Calculate target temperatures for tempering dark, milk, and white chocolate.

Chocolate Coating Calculator

Calculate how much melted chocolate you need to coat truffles, biscuits, or fruit by quantity.

Sugar Syrup Stage Calculator

Look up temperatures and sugar concentrations for each candy-making stage.

Buttercream Calculator

Calculate butter, icing sugar, and milk quantities for buttercream by cake size and coverage.

Fudge Calculator

Calculate sugar, butter, milk, and chocolate quantities for fudge by batch size.

Last updated: February 2026

All calculations are based on standard ratios and conversions. Results may vary with specific ingredients, equipment, and conditions.