Please help- want to increase quantities but unsure how to adjust cake tin size?!

[letsbehonest100]

I have a recipe for an 8 inch square tin. I need to make a bigger cake, so I thought I'd increase the quantities by half.

I had assumed that this would mean I needed a 12 inch tin- but after a quick google I'm now confused as apparently its not that simple!

Can anyone advise me as to what size of tin I need.

Also, cooking time is an hour (choc cake), I'm not very sure how much to increase cooking time by and again would really appreciate advice.

It is easy to work out when you remember that the measurement is all about what is going into the tin - not around the edges of it

You get the answer by working out the square:

8" x 8" = 64 square inches
12" x 12" = 144 square inches. More than twice as big!

You want something approx 96 square inches (1.5 x the size of the 8" square) so a 10" square (100 square inches) would be just about right.

Time depends so much on the oven.
For non fan, add on about half the original cooking time.
For fan - personal experience says add a third and then keep checking, as they cook much faster

Increasing the cooking time is one thing, but getting the heat in to the middle of the cake takes longer, the larger you go. There is a risk that the outside of the cake may get a little crisp before the middle is completely cooked. Putting a cake cone (inverted aluminium cone) in the middle of the cake would draw the heat in and cut the cooking time. Instead of the middle of the cake being 5 inches from a heat source (on a 10" square cake), the furthest any part of the cake would be away from a heat source would be about half that. The cake would be more evenly baked.