Excel formula to convert weight quantites

[Get the cans out]

Im trying to do a formula in excel to weigh out the right amount of sugarpaste for a cake.

[FDibbins]

Get the Cans Out, welcome to the forum

well to begin with, i think the marzipan forumula should be...
=B6/3.1416*C6/1000 6 cakes at 15 grams is not 28.65 kilograms
2nd, what is the formula to calc the sugarpaste?

[Get the cans out]

Thats the problem i dont know how to do the formula the cake is 6 inch diameter and 3 inches deep.So by my reckoning the cake would be 12 inches if flat + 4inchs for board so that should be 14 inchs is that right?
A 6 inch cake with a 5mm drop has .5 kg or 500g
so im trying to do a formula with a 6 inch cake with 3 inch drop and 2 inch lip around cake so 6+3+3+2+2=16 inches if the whole thing was flat (rolling out paste) should cover cake

[Get the cans out]

Here is my spreadsheet

[Get the cans out]

What i want to do is on the cake reckoner tab is insert cake size in say A1, select from a dropdown list square,round,hexagon etc shaped cake in B1 and in C 1 the weight in grams is automatically inserted.
I know i could insert them all manually BUT what is the fun in that