How to Scale a Recipe to fit a Different Sized Tin

red velvet cake

One of the most frequently asked questions that we get at Partyanimalonline is how to scale a recipe up or down to fit a different sized tin particularly for our Rich Fruit Cake Recipe. We’ve all been in the position where we have found ‘the perfect recipe’ but it is only available in one size and we really need it for a wedding cake we have been asked for so how can we change the recipe to fit the tin we need?

This does require some maths to do properly so go get your calculator!

Although in the case of the Fruit Cake Recipe there is a sizing table for the most common sizes giving the ingredients so you don’t need to do the calculations!

The thing that makes the difference is the surface area of the cake that you want to bake.

Scale a recipe for Square Cakes

To find out the surface area of the cake, before you can scale a recipe, you need to do a bit of basic calculation. For square or rectangular cakes this is very straightforward. It is simply multiplying the 2 sides to get a square inch figure.

So if you have an 8” square you need to multiply 8 x 8 to give the surface area in square inches

8” X 8” = 64 square inches.

And a 4” square cake is

4” x 4” = 16 square inches.

This shows that a 4” cake is one quarter the size of an 8” one. (64/16= 4)

Are you with me so far?

It is easy to assume that a 4” cake would be half the size of an 8” but if you look at the diagram you can see that this is not the case. This is pretty straightforward in that if you have a recipe for an 8” square cake you need to divide all the quantities by 4 to give a 4” cake. This becomes more difficult when the sizes are not so obvious however by working out the surface area you can work out the proportion you will need with just a little extra calculation.

So The recipe you have is for an 8” square cake and you want to make a 6” square cake it becomes a little more difficult to visualise the proportion so you need to calculate the surface area for each cake so

8 x 8 =64

6 x 6 = 36

To get the quantities you need you firstly need to find the proportion.

If you divide the size you want by the recipe size you have.

36/64 you get 0.56 from this you can see that you will need just over half the recipe quantity for your 6” tin.

I will use a Victoria sponge recipe to demonstrate.

The 8” recipe needs

  • 100g flour
  • 100g margarine
  • 100g sugar
  • 2 medium eggs

So multiply each of these quantities by 0.56 to get the new recipe

100 x 0.56 = 56g so you will need about 56g of sugar flour and butter and just over 1 egg (obviously it is difficult to make the eggs accurate however I would use a large egg instead of medium to get the slightly larger egg quantity that I need.

It doesn’t matter what your recipe is as long as you use this calculation on each ingredient in turn you will end up with the perfect scaled recipe to fit a 6” tin.

To try a different size – If you want your 8” recipe to make a 10” square tin

8 x 8 = 64

10 x 10 = 100

So you divide 100 by 64 and you get 1.56 (This is slightly over 1 ½ times the recipe)

Taking the 100g of flour and multiply it by 1.56 you get 156g flour  and 3.12 eggs (again using a larger size of egg will give you more egg per egg used to satisfy the recipe. For more accuracy you can break the eggs into a bowl and weigh them and then use the weight (most medium eggs are around 50g)

To give you a start here is a table of surface area of different squared cakes.

Square tin size Round tin size calculation Surface area
4” 5” 4 x 4= 16 16
5” 6” 5 x 5 = 25 25
6” 7” 6 x 6 = 36 36
7” 8” 7 x 7 = 49 49
8” 9” 8 x 8 = 64 64
9” 10” 9 x 9 = 81 81
10” 11” 10 x10 = 100 100
11” 12” 11 x 11 = 121 121
12” 13” 12 x 12 =144 144

So assuming your recipe is for an 8” square cake to get the new size look up the surface area of the tin size you want a recipe for and divide it by 64 for the 8” square cake and this will give you the figure that you need to divide you ingredients by. So for an 11” square cake you need to divide 121/64 which gives you 1.89 which means you need to multiply all your ingredients by1.89 to get the new recipe so

100g x1.89 = 189 g

2 eggs1.89 = 3.6 (nearly 4 eggs so again use a slightly different sized egg eg 4 small eggs to make the quantity right.

Rectangular Cakes

These are the same as working with square cakes in that you need to multiply the short side by the long side to get the surface area. So for a 10 x 8 rectangular tin the area is 10 x 8 or 80 square inches. All other calculations to scale the recipe remain the same.

You may have noticed that the surface area of this tin is almost identical to a 9” square tin so you will find that if you add the 2 sides of a rectangle up and divide by 2 this will give you the equivalent in a square tin. So a 14 x 12 rectangle is about the same as a 13” square tin.

I knew those school maths lessons would be useful one day! I hope you haven’t gone to sleep!

Scale a recipe for Round Cakes

scaling recipes

Here we get a bit more complicated when trying to scale a recipe and need one of those geometry formulae to get an exact size.

 The formula we need = π r². (pi r squared)

Pi = 3.12

 r = radius which is half way across the circle size so for an 8” cake tin the r = 4” so

3.12 x 4 x 4 = 49.92 almost the same as for a 7” square cake.

For a 12” round cake we times 3.12 x 6 x 6 = 112.36

So for the sake of recipe scaling you can assume that a round cake is the same surface area as a square cake that is one inch smaller on each side. In other words, an 8” round cake is the same as a 7” square cake and a 10” round cake is the same as a 9” square cake. This is not totally accurate, but it saves some calculations and the difference just gives a slightly deeper or shallower cake!

The way of working out is the same as before.

Take the size of tin you want to make and divide by the tin size for your recipe then multiply all you ingredients by that fraction. So to make an 9” round  recipe fit a 10” round tin  81/64 = 1.26 thus your flour, sugar and fat in our Victoria sponge recipe would scale from 100g to 126g and you would need 2.5 eggs.

Scaling for Hexagonal Cakes

If you measure the diameter of the hexagonal tin at the widest (points) and the smallest (flat sides) add them together and divide by 2 you will find the average diameter of the tin – you can then treat this the same as a round cake. If you use the smallest measurement you will get a cake that is a bit deeper and the widest will give a slightly shallower cake than the original round recipe.


I know this has been a bit of a technical blog and I’m sure most of you now have headaches trying to process it, but it is well worth the effort because you can use any recipe for any sized cake and scale the recipe up or down to any other size or shape you like and as long as you can work out the surface area of the cake tin you are not reliant on finding the right sized recipe any more but can use any recipe.

Although I have used inches in this blog it works just as well in cm or mm whichever you work best with.

The only additional thing to bear in mind is your baking time although this is more about the depth of the cake which stays the same in each case rather than the width of the cake though you may find that larger cakes take a little longer or need a slightly higher temperature to bake thoroughly.

The other good thing about this method is that you can scale a recipe from a round to a rectangular or any other geometric tin you like but still be be sure that your finished cake will be the same depth and taste as the original cake recipe. All you need is the calculations and a calculator to help with the maths and just make sure you use the same calculation on every ingredient in your recipe.

If you want some fabulous cake tins for your new scaled up or down recipe check out our range on the Partyanimalonline shop. My personal preference has always been for the Invicta tins – expensive at first but mine have lasted more than 20 years so well worth the investment. Or as an alternative we have PME tins which are very good and have loose bottoms to make removing your cake easier.

Good luck trying to scale your recipes and try to love your maths and your baking!

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