Can anyone help me? I'm making Delia Smith's rich fruit cake for my wedding in July but her recipe's only go up to 11" and I need to make a 12" tier. I've tried converting it myself but just can't seem to work it out. Does anyone know how to scale it up or where I could find out?
Thank you!!

Hi Heather,
This is what I do and it works everytime. It's Spanish maths so I don't know if you have this method here. If for example you need 300g of flour for an 11" cake tin and you want to increase it to 12" you do as follows:

11" ------------------ 300g
12" ------------------ x

12 x 300
x = ---------- = 327.3 (round it up to 327g)
11

Do this for every single ingredient and the cooking time. If you are unsure of the formula just let me know or post the measurements and I'll calculate it for you.

P.S.If the first decimal after the dot is between 0 and 4 then leave the number before the dot as is. If it is however between 5 and 9 then round the number up by 1 so for example if the result was 327.5 you would round it up to 328.

Heather - the formula for the volume of cylinder is (approximately) 3.14 multipled by the square of the radius and the height of the cylinder.

You need to know the ratio of the volumes so that you can multiply the amount of the ingredients. So, for an 11 inch tin, the volume is

3.14 x 5.5 x 5.5 x H

Assuming the 12 inch cake tin is the same height, the volume will be

3.14 x 6 x 6. x H

and the ratio will be 36/30.25 or about 1.2 - so you need 20% more ingredients (or one fifth extra) to make the larger cake.

If the heights are different, you will need (36 x (height of 12inch tin))divided by (30.25 x (height of 11 inch tin). So if the 12inch tin is 4.5 inches high, and the 11 inch tin is 4 inches high, the formula is

(36/4.5) divided by (30.25/4) which is aproximately 33% or one third more.

You will have to cook it for a longer time, but be careful not to burn it - cook slowly and cover with brown paper if it looks like it is going to catch.

Best of luck

Kirsten

I tabbed the formula but when posting it it hasn't kept the format.

12 x 300 / 11 = 327.3

whoops I meant (36 x 4.5) divided by (30.25 x 4)

Sorry Heather I'm probably confusing you but forgot to menthion that when you calculate the ccoking time make sure that you convert it to minutes before carrying out the calculation, so if for an 11" you need to cook it for 1 hour just enter it in the formula as 60 min.

Heather - I assumed your cake was round, but exactly the same calculation applies if it is square, because the volume of the cake tin is base times width times height so if

11" square 11 x 11 x H
12" square 12 x 12 x h

and the ratio you need will be ((12x12xh) divided by (11x11xH))

so using the same numbers (144x4.5) divided by (121x4) = 1.33 or 33% extra mixture needed.

If the heights of the tins is the same, the ratio will be 144/121 or 1.2 (i.e. 20% more again)

I love Maria dearly, but I don't think her method will give you enough mixture as the ratio of the size of the tins is based on a square relationship not a simple ratio of the sides/diameters of the tins.

I should say it obviously doesn't matter so much for you Heather which way you do it if your tins are the same height, although if the difference in the diameter/sides of the tins was more than nominal (here it is less than 10%) it would make a significant difference.

Also - Heather - you must be excited! I hope your wedding day is a lovely sunny success, it all goes well and that you will both be very happy in your life together.

I am very confused it looks like you need a degree in maths to fathom this one out. How about dry ingredients divide by 11 and times by 12 will this work??Or is this what you have been saying all along??

Divide 11 and times 12 is Maria's method - which will probably work for Heather if the height of the tin is the same - otherwise, it won't give big enough increase. For example, if the recipe was for an 8 inch cake, and you wanted to do a 12 inch one, divide 8 times 12 would leave you seriously short of mixture and with a cake like a pancake - and probably burned as well.

I am not an expert cake maker, nor do I have a degree in math - but what I would do personally is make double or maybe 1 1/2 times the mixture and fill my cake tins to the normal level - forgive me if I'm wrong but rich fruit cake ie christmas cake which I assume the recipie is for the wedding cake does not rise (or hardly at all) and if you have mixture left over make another small cake for another occasion.

Like I said I'm no expert just a make it up as I go cook - but maybe to experiment without costing too much make and bake a small quantity first to try out.

i'm having the same problem - i have successfully made several 8" christmas cakes and i ill-advisedly offered to make my mate's wedding cake, 3 tier, 12" 8" and 6" (are these acceptable differences?) now i'm worried for the same conversion reasons - i got the equation of a cylinder but i also remember my biology teacher saying that for reasons of physics it's not possible for an ant to grow to the size of an elephant. do these rules also apply to increasing a cake size from 8" to 12"? and i'd assumed to need around 7 hours to bake it. also, will the smaller two cakes bake in line with the larger if they are on ...which shelf? larger or smaller higher? i wish i hadn't bothered now

oskar (2, because they forced me)

Not sure if this will help, but there is a discussion about 3 tier wedding cakes here. [link]

I have a recipe for 6" 8" 10" and 12" tins equivielent to 7" 9" 11"and 13" round cakes. there is s huge difference between sizes e g for 10" 1 lb 2oz butter and 12" 2 lb 2oz butter.

I have been asked to make a 4 tier wedding cake (fruit) to serve 200 people, daunting I know! Does anyone have any idea what sizes I should do, and how to cost this???

To calculate a mix for a 6 inch cake tin to a 12 inch cake tin is easy.

we are using a 6" cake tin with a height of 5"
12" cake tin with a height of 5"

first calculate the volume of the 6" tin like this
pi r2xh thats 3.1415 x radius x radius x height) so

3.1415 x 3 x 3 x 5 = 141.36

then calculate the 12" tin in the same way

3.1415 x 6 x 6 x 5 = 565.50

then devide the 12" volume into the 6" volume , thats 565.50 /141.36 = 4.

So use 4 time the recipe. alter the cooking times and there you are.

use this to calculate any volume. i have used this and it works.

Good luck

MadBrit