Adjusting ingredient quantities

[stopthenoise]

I need some help adjusting a recipe for a larger cake please. I usually bake basic cakes for family using a Mary Berry recipe that's never failed me yet. It makes a decent sized 2 layer 8 inch cake, ingredients are:
4 eggs
225g of butter, sugar and flour
2tsp baking powder
I need a 3, possibly 4, layer cake. The layers come out quite deep anyway so could probably get away with 3. How do I adjust the quantities from my trusty 2 layer recipe? TIA

Use six or eight eggs for 3/4 layers. Weigh the eggs before you start (in their shells) and use that amount of flour, sugar and butter. Alternatively, do what you're used to but twice and you'll have 4 layers!

stop, i use exactly the same quantities as you , in fact i just finished making 3 cake all different flavours, i bought the same size tin so i could make 3 layers and all i do is add another 4 ozs, to make a 12 oz mix, then you have a 4oz mix in 3 tins( 225grms is an 8 oz mix, but i guess you know that) .

I make cakes for a local cafe and i always use the same mix and quantites, the only difference i do is with the choc cake where i add melted dark choc as well as cocoa powder.