How many batches of buttercream is that?

A standard American buttercream made with one pound of butter and two pounds of icing sugar yields roughly five cups, so a two layer 8 inch cake needing 5.5 cups is a little over one batch. Swiss meringue yields more per pound of butter because it is lighter, and a whipped ganache yields less again.

Do I really need a crumb coat?

On any cake you want to look clean, yes. The crumb coat is a thin layer whose only job is to trap loose crumbs so the final coat goes over sealed cake rather than bare crumb. Skip it and you will drag brown flecks through the finish however careful you are. It costs about an eighth of an inch of buttercream and half an hour in the fridge.

How much more does a rosette-covered cake need?

Roughly 60 percent more than a smooth coat with borders, because a piped surface uses far more buttercream than a scraped one. The exact figure varies enormously with tip size: a large open star lays down a lot of buttercream per rosette, and covering a whole side in them is closer to sculpting than to frosting.

Why does the calculator ask how many layers?

Because layers change the side area and add filling, and side is where most of the frosting goes. Going from two layers to three on an 8 inch cake increases the side area by roughly half and adds another filling gap. The top area does not change at all, since the cake is no wider than it was.

Frosting and finishing

Frosting Quantity Calculator

Buttercream needed for any cake, from its real surface area, for every finish from naked to fully piped.

Quick answer

A two layer 8 inch round cake takes about 5.5 cups of buttercream, roughly 2.8 lb. That covers a crumb coat and a final coat over 93 square inches of side and 50 of top, plus filling between the layers and a fifth again for piped borders.

Cake size

Layers

Finish

Result

5 1/2 cups of buttercream

about 2.8 lb, for a 2 layer cake standing 3.71 in tall

Every figure, with what it is based on
Figure	Value	Basis
Buttercream needed	5.5 cups (2.8 lb)	Derived area, convention thickness
American buttercream batches	About 1.1 At roughly 5 cups per pound of butter	Trade convention
Side area to cover	93.2 sq in	Derived
Top area to cover	50.3 sq in	Derived
Filling between layers	50.3 sq in	Derived

(93.2 + 50.3) x 0.375 + 50.3 x 0.25, in cubic inches

The areas are derived from the cake dimensions. The coat thicknesses, an eighth of an inch for a crumb coat and a quarter for the final coat, are trade conventions and shops differ on them. Make a little more than this figure: what stays in the bowl, on the paddle and in the bag adds up to most of a cup.

The formula

volume = (side area + top area) x coat thickness + filling area x filling thickness

This is surface area multiplied by coat thickness, which is why it gives a real number rather than a rule of thumb. The side area is the perimeter times the finished cake height, the top is the pan area, and the filling is the pan area times the number of gaps between layers.

Make more than the calculated figure. What stays in the bowl, on the paddle and in the piping bag adds up to most of a cup on a cake this size, and a batch that comes out exactly to the arithmetic will run short.

Derived, published or convention?

The surface areas are DERIVED from the cake dimensions. The coat thicknesses, an eighth of an inch for a crumb coat and a quarter for the final coat and the filling, are TRADE CONVENTION and shops differ on them.

Buttercream for a two layer cake, smooth coat with borders
Cake	Side area (sq in)	Top area (sq in)	Buttercream (cups)	Roughly (lb)
6 in round	69.9	28.3	3.6	1.8
8 in round	93.2	50.3	5.5	2.8
9 in round	104.9	63.6	6.6	3.3
10 in round	116.6	78.5	7.7	3.9
12 in round	139.9	113.1	10.2	5.1
8 x 8 in square	118.7	64	7	3.5
9 x 13 in rectangle	163.2	117	11.2	5.6

Areas derived from the cake dimensions; coat thicknesses are trade convention. A standard American buttercream made from one pound of butter yields roughly five cups.

Gear for these numbers

These are rendered from the verified catalog and re-ordered against your numbers once you calculate.

Intermediate

KitchenAid

KitchenAid KFE5TS Flex Edge Beater for 4.5 and 5 Quart Tilt-Head Mixers

$49.99

A flexible silicone edge that wipes the bowl wall as it turns, which is the single attachment that most improves buttercream, because unmixed butter clinging to the side is what makes a batch look curdled.

Best for: buttercream and creaming butter and sugar

Check price on Amazon

Amazon prices move often, so check before you buy.

Beginner

Ateco

Ateco Stainless Handle Bench Scraper, 5.9 x 3 in

$9.99

A straight stiff edge held vertical against a turning cake is how a sharp buttercream side is made, and a bench scraper does it better than a curved comb.

Best for: sharp-edged buttercream

Check price on Amazon

Amazon prices move often, so check before you buy.

Expert

Ateco

Ateco Revolving Cake Decorating Stand, Aluminum Turntable with Cast Iron Base

$68.26

The cast iron base is the whole point: a heavy turntable keeps spinning at a steady speed while you hold a scraper still, which is what produces a smooth side.

Best for: smooth buttercream sides

Check price on Amazon

Amazon prices move often, so check before you buy.

Questions people ask

How many batches of buttercream is that?: A standard American buttercream made with one pound of butter and two pounds of icing sugar yields roughly five cups, so a two layer 8 inch cake needing 5.5 cups is a little over one batch. Swiss meringue yields more per pound of butter because it is lighter, and a whipped ganache yields less again.
Do I really need a crumb coat?: On any cake you want to look clean, yes. The crumb coat is a thin layer whose only job is to trap loose crumbs so the final coat goes over sealed cake rather than bare crumb. Skip it and you will drag brown flecks through the finish however careful you are. It costs about an eighth of an inch of buttercream and half an hour in the fridge.
How much more does a rosette-covered cake need?: Roughly 60 percent more than a smooth coat with borders, because a piped surface uses far more buttercream than a scraped one. The exact figure varies enormously with tip size: a large open star lays down a lot of buttercream per rosette, and covering a whole side in them is closer to sculpting than to frosting.
Why does the calculator ask how many layers?: Because layers change the side area and add filling, and side is where most of the frosting goes. Going from two layers to three on an 8 inch cake increases the side area by roughly half and adds another filling gap. The top area does not change at all, since the cake is no wider than it was.

Worked out for you already

A note on what this can and cannot tell you

This calculator does arithmetic on the numbers you give it. It does not know your oven, your recipe or your altitude. Figures are labelled as derived, published or trade convention, and where no honest figure exists the calculator says so instead of producing one. Researched guidance, not professional advice.