I want to change the size of a cake, i want two smaller cakes from a recipe that calls for a nine in pan. How can i figure out what size to use

Once again, Alice to the rescue! https://food52.com/blog/13239-how-to-make-your-baking-recipe-fit-your-pan-size

A 9" pan has a volume of 8-10 cups (depending on if round, square or spring form).
An 8x4" loaf pan has about 4c capacity; so 2 of those might do. Or maybe 8" round pabs, but they'd be bigger than you need (about 6 cup each).
Or, you could make the original, cut in two layers and present each as a cake...frosted or dusted with icing sugar.