Cake – Meringue Imitation to practice decoration

A 9" round pan that is 1 1/2" deep takes 6 cups of batter, while one that is 2" deep takes 8. That's for totally full to the brim. This source says about the amount of batter from a box:

An average 2-layer cake mix yields 4 to 5 1/2 cups of batter.

and should have a bunch of helpful guides to using batter for non-standard pans.

Both solutions will work.

If you are making more mering, then make sure the thickness of the meringue layer in stays the same as for the small tin. If you scale the recipe correctly this happens automatically.

I think your math is off though. The area of your 24 inch tin is only 1.77 times larger than the 18 inch pan.

Assuming your pan is round: The area of the large pan is pi*24^2 and the area of the small is pi*18^2 the ratio is therefore pi*24^2 / pi*18^2 = 24^2 / 18^2 = (24/18)^2 = 1.77 .

If your pan is square the (almost) same computation will give the same result.