CakeyTops
Free Tool

Fondant Calculator

Work out how much fondant you need to cover your cake, how wide to roll it out, and how much to buy. Handles single cakes and multiple tiers at three thicknesses.

Tier 1

Total Fondant Needed

813g

1.8 lbs

Tier 1 — 8" round

Weight813g
Roll To18" / 46cm

How much fondant to cover a cake — chart

Fondant needed for a round cake 4 inches tall, by rolled thickness. Standard is 4mm and is what you want for almost every covered cake. The roll-out column is the circle you need to roll before draping — measure it, do not guess it.

Fondant weight needed by cake size and thickness, with roll-out diameter
Cake sizeThin (2.5mm)Standard (4mm)Thick (5mm)Roll out to
4" round328g492g656g14" / 36cm
6" round428g642g857g16" / 41cm
8" round542g813g1084g18" / 46cm
10" round669g1004g1339g20" / 51cm
12" round810g1215g1620g22" / 56cm

Taller cakes need more. Enter your actual height in the calculator rather than reading off this chart if your tiers are deeper than 4 inches.

How the quantity is worked out

Most fondant charts underestimate, because they measure the cake rather than the fondant. The cake's surface area is not what you need to buy — you cannot drape a shape that size over a cake without it tearing at the corners.

What you actually roll is a circle wide enough to reach the board on every side: the cake diameter, plus twice its height for the two sides it has to travel down, plus roughly 2 inches for tucking under and trimming. The calculator works out the volume of that whole disc at your chosen thickness, then multiplies by the density of fondant, about 1.3g per cubic centimetre.

You will trim a fair amount off. That offcut is not waste — knead it back into a ball, double-wrap it in cling film and it keeps for months in an airtight box at room temperature. What matters is that you started with a disc big enough, because a piece that comes up an inch short at the bottom cannot be rescued.

Frequently Asked Questions

How much fondant do I need to cover an 8 inch cake?

A 4 inch tall, 8 inch round cake takes about 815g of fondant rolled to a standard 4mm, and you roll it out to an 18 inch (46cm) circle. At a thinner 2.5mm you can drop to around 540g, and a thicker 5mm finish needs about 1,085g. Buying a 1kg block for a single 8 inch cake is the sensible call.

How much fondant to cover a 6 inch cake?

Around 640g at a standard 4mm thickness for a 4 inch tall cake, rolled out to a 16 inch (41cm) circle. A 500g block will not stretch to it once you allow for trimming, so buy 1kg.

How much fondant to cover a 10 inch cake?

About 1,005g at a standard 4mm for a 4 inch tall cake, rolled to a 20 inch (51cm) circle. For a 12 inch, budget around 1,215g rolled to 22 inches (56cm).

Why is the figure higher than the cake’s surface area suggests?

Because you cannot cover a cake with a piece of fondant that exactly matches its surface area. You roll a full circle wide enough to drape over the top and all the way down the sides, then trim the excess away. The calculator sizes the disc you actually have to roll, which is why it comes out higher than an area-based estimate and why you always end up with offcuts.

What diameter do I roll fondant out to?

Cake diameter plus twice the cake height, plus about 2 inches for tucking and trimming. An 8 inch cake that is 4 inches tall needs an 18 inch circle. Mark the diameter on your work surface before you start rolling — it is much easier than judging it by eye and re-rolling.

How thick should fondant be on a cake?

About 4mm is the standard for a covered cake. Thinner than 3mm and every imperfection in the ganache or buttercream underneath shows through, and it tears while you smooth it. Thicker than 5mm and it starts to taste like a mouthful of icing. Use thin only for plaques, cut-outs and decorations.

How much fondant do I need for a tiered cake?

Work each tier out separately and add them together — the calculator does this for you when you add tiers. Do not roll one huge piece for multiple tiers; each tier gets its own covering, and rolling one oversized sheet is how fondant tears under its own weight.

Should I ganache or buttercream under fondant?

Ganache gives sharper edges and a firmer surface for the fondant to sit against, which is why most decorators use it for anything structured. Buttercream is softer and more forgiving to apply but shows more movement under the fondant, especially in warm weather.

Ganaching the cake first for sharper edges? The ganache calculator works out how much you need under fondant, and splits it into chocolate and cream. For a buttercream finish instead, use the buttercream calculator.

Finishing the cake off? Design and print a matching custom cake topper at 300 DPI, free.

Recommended Supply

Colour your fondant

Knead a little concentrated gel paste into white fondant for deep, even colour without the stickiness liquid colour causes. A small set covers most shades you'll need to mix.

Affiliate disclosure: As an Amazon Associate I earn from qualifying purchases.
Used in our kitchenDecorating supplies

Sugarflair Rainbow Gel Food Colours (Set of 6)

Six concentrated gel food colours for buttercream, royal icing, sugarpaste, and cookie painting.

Sugarflair is a UK decorating staple. This six-colour starter set is highly concentrated, so a cocktail-stick dab goes a long way, and the colours deepen as they dry — which is exactly what you want for strong buttercream tones and deep PYO palette colours that still read after a wet brush.

Why we recommend it

The set we would point a new decorator to before they commit to forty individual pots — enough to mix most shades you actually need.

  • Colouring buttercream, royal icing, and sugarpaste
  • Mixing custom shades from a small core set
  • Deep colours for paint-your-own palettes
Amazon product reference: B00K5SUR50
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