Help with birthday cake mix please!!

[girliefriend]

My dd wants a treasure island bday cake, have got a bday cake book which shows you how to decorate it but doesn't give me quantities for ingredients.

I will be looking to bake it in a dish which is 20cm x 26cm, depth 6cm. Just a plain vanilla sponge, can anyone hazard a guess at what quantities of ingredients I would need?

Picture of what the cake should look like hopefully

www.cakebaker.co.uk/apps-for-bakers/baking-tin-size-conversion-calculator/

For that size I would use a 10 egg madeira mix (10 eggs, 500g sugar, butter and SR flour, 2 tsp baking powder) mix as you would for a Victoria sponge and bake in 2 tins @ 160 for about an hour. If you only have 1 tin, check after about an hour and test every 10 mins. Good luck

Thankyou in the end I went with double the quantities recommended for one butter cake mix, turned out really well.

Adara that link is brilliant thanks