Quick answer
The fondant disc has to reach the cake's width plus twice its height plus a margin to hold and trim, about 18.4 inches across for a two layer 8 inch cake, using roughly 26 ounces of fondant. Fondant should never go in the fridge once it covers a cake, since condensation forming on the cold surface makes it sticky.
Satin Ice Fondant for Cake Decorating, White, 5 lb
Five pounds covers roughly three 8 inch cakes with trim to spare, and Satin Ice rolls thinner before tearing than the fondant that comes in a decorating kit.
Best for: covering several cakes, or one large tiered cake
Check price on AmazonFondant coverage is a straightforward geometry problem once you stop guessing at it. The rolled disc has to reach across the top of the cake, down one side, across the bottom, up the other side, and leave a little extra to hold onto and trim, which comes out to the cake's diameter plus twice its height plus a margin of about an inch and a half on each side. A two layer 8 inch cake stands about 3.71 inches tall once it is filled and coated, which puts the disc at roughly 18.4 inches across and uses about 26 ounces, or 1.6 pounds, of fondant rolled to the standard eighth-inch working thickness.
The other rule worth knowing before you start is about storage, not geometry: a fondant covered cake should never go into the fridge. A cold surface returning to a warmer room sweats condensation, and that moisture is what turns a smooth fondant coat sticky and dull rather than crisp. The table below gives the disc size and weight for common cake sizes, computed the same way the fondant calculator works it out, so you can check the amount before you buy.
How much fondant do I need for my cake size?
Every figure below comes from the same formula: disc diameter equals the cake's width plus twice its finished height plus a 1.5 inch margin on each side, rolled at an eighth of an inch thick, using rolled fondant's published density of about 1.35 grams per cubic centimeter.
| Cake | Height (in) | Disc diameter (in) | Fondant (oz) | Fondant (lb) |
|---|---|---|---|---|
| 6 in round, 2 layers | 3.71 | 16.4 | 20.6 | 1.29 |
| 8 in round, 2 layers | 3.71 | 18.4 | 25.9 | 1.62 |
| 9 in round, 2 layers | 3.71 | 19.4 | 28.8 | 1.80 |
| 10 in round, 2 layers | 3.71 | 20.4 | 31.9 | 1.99 |
| 12 in round, 2 layers | 3.71 | 22.4 | 38.4 | 2.40 |
| 8 in round, 3 layers | 5.69 | 22.4 | 38.4 | 2.40 |
| 10 in round, 3 layers | 5.69 | 24.4 | 45.6 | 2.85 |
How do you cover a cake in fondant step by step?
- Chill the crumb-coated cake just until the buttercream underneath is firm to the touch, no more than 15 to 20 minutes in a cool kitchen, since fondant needs a barely-tacky surface to grip rather than a fully hardened one.
- Knead the fondant until it is smooth and pliable and shows no cracks at the edges when folded, working in a little vegetable shortening if it feels dry or stiff.
- Roll it out on a lightly cornstarch dusted surface or a silicone mat such as OXO Good Grips Silicone Baking Mat, 11.5 x 16.5 in to about an eighth of an inch thick, checking the diameter against the cake size in the table above.
- Lift the rolled disc onto a rolling pin and unroll it centered over the cake in one motion, since repositioning a large sheet of fondant tears it far more often than a clean first drape does.
- Smooth the top first with the flat of a hand, working any trapped air toward the edge before it has a chance to travel down the sides.
- Work down the sides in overlapping strokes with a fondant smoother such as Ateco 1301 Fondant and Icing Smoother, easing out folds at the base rather than stretching the fondant thin trying to erase them.
- Trim the excess at the base with a sharp knife or a pizza cutter held flat against the board, leaving a clean edge rather than a bunched skirt of extra fondant.
- Press the bottom edge in gently with the flat side of the smoother to seal it against the board, then let the covered cake sit uncovered at room temperature until the surface firms.
Why can’t a fondant covered cake go in the fridge?
Because a cold surface sweats when it warms back up, the same way a cold glass of water beads on the outside on a humid day. A fondant covered cake taken from the fridge does exactly that as it returns to room temperature, and the moisture that forms directly on the fondant is what turns a smooth, matte coat sticky and dull. This is a physical property of fondant rather than anything specific to one brand or recipe.
If a filling genuinely needs refrigeration, such as a fresh fruit filling or a cream cheese layer, chill the cake before it gets covered in fondant, not after. Once the fondant is on, keep the finished cake at room temperature in a box with a little airflow rather than sealed airtight, and treat the covering itself as shelf-stable decoration rather than something that needs cooling.
Before this cake leaves the kitchen
The fondant covering itself does not need refrigeration, but whatever is underneath it might. Cream cheese and whipped cream fillings still need the same refrigeration they would need under any other frosting, so chill the finished cake ahead of serving if the filling calls for it, and let it sit briefly at room temperature before cutting so the fondant is not cold and stiff. Ask about allergies before you start if you are baking for someone else, since cross contact happens at the mixing bowl and the rolling surface, not at the table. And if a cake is being sold rather than given away, check your state's cottage food law first, since rules on covered and filled cakes vary a great deal from one state to the next.
What goes wrong covering a cake in fondant?
| Problem | Likely cause | Fix |
|---|---|---|
| Fondant tears while draping | Rolled too thin for its size, or lifted and repositioned more than once | Roll a bit thicker for a large cake, and drape it in one motion rather than adjusting the sheet after it touches the cake |
| Fondant looks lumpy or uneven over the sides | Air trapped underneath before smoothing began at the top | Smooth the top completely first, then work down the sides in one direction to push trapped air out at the base |
| Surface turns sticky and wet | The covered cake went into the fridge | Keep a fondant covered cake at room temperature; if a perishable filling needs the fridge, chill it before covering rather than after |
| Fondant cracks at the base or around a sharp corner | Fondant was cold, dry, or rolled too thin for that spot | Knead in a little shortening to soften it, and roll a touch thicker anywhere the cake has a hard edge, such as a square tier’s corner |
| Color looks patchy after tinting | Gel color worked in unevenly, or a liquid color used instead | Knead gel color in fully before rolling, and use a gel or paste color rather than a liquid one, which can make the fondant sticky |
What this job actually needs
Satin Ice Fondant for Cake Decorating, White, 5 lb
$34.99Five pounds covers roughly three 8 inch cakes with trim to spare, and Satin Ice rolls thinner before tearing than the fondant that comes in a decorating kit.
Best for: covering several cakes, or one large tiered cake
Check price on AmazonAmazon prices move often, so check before you buy.
Ateco 1301 Fondant and Icing Smoother
$7.94The fondant smoother from a trade supplier rather than an unbranded two pack, with a flat face and a square corner for pressing the bottom edge in.
Best for: finishing a fondant covering
Check price on AmazonAmazon prices move often, so check before you buy.
OXO Good Grips Silicone Baking Mat, 11.5 x 16.5 in
$24.95Cut to the half sheet, and the surface a rolled fondant or a macaron sheet wants, because it releases without the flour that dries fondant out.
Best for: rolling fondant and baking sheet work
Check price on AmazonAmazon prices move often, so check before you buy.
Questions people ask
- How much fondant do I need for an 8 inch cake?
- About 26 ounces, or 1.6 pounds, for a standard two layer 8 inch round cake about 3.7 inches tall, rolled at an eighth of an inch thick. That figure comes from a disc roughly 18.4 inches across, sized to reach the cake's width plus twice its height plus a margin to hold and trim while covering it.
- Why can’t a fondant covered cake go in the fridge?
- Because a cold fondant surface returning to a warmer room sweats condensation, and that moisture makes the fondant sticky and dull rather than smooth. If a filling genuinely needs refrigeration, chill the cake before it gets covered, then keep the finished, fondant covered cake at room temperature rather than cooling it afterward.
- How thick should fondant be rolled?
- About an eighth of an inch is the standard working thickness: thin enough to drape smoothly and show detail, thick enough to resist tearing on the way to the cake and hold up over corners. Rolling noticeably thinner saves fondant but raises the risk of tearing, especially over a square tier's sharp edge.
- Why does my fondant tear when I lift it onto the cake?
- Usually because it was rolled too thin for the cake's size, or because it was lifted and repositioned more than once after touching the surface. Roll a bit thicker for a large cake, drape it centered in one motion using a rolling pin to lift and unroll it, and avoid dragging it sideways once it has made contact.
- Can I put fondant on a cake with a dairy filling?
- The fondant covering itself is shelf-stable, but whatever sits underneath it, such as a cream cheese or whipped filling, still needs the same refrigeration it would need under any other frosting. Chill the finished cake before serving if the filling calls for it, and let it sit at room temperature briefly before cutting so the fondant is not cold and stiff.
Related pages
How this page was put together
Researched from pan geometry, published manufacturer capacities, published serving conventions and university extension guidance. Not hands-on testing, and not professional advice.
Figures are labelled as derived, published or trade convention. Where no honest figure exists, the page says so rather than filling the gap.