I want to make My mom's pineapple upside down cake in a 13x9 pan rather than the suggested 9 inch skillet. How should I change the recipe? Should I make 1.5 recipes? Or 2?
You should double it.
Agree with Smaug...the rectangle pan holds 15c volune, while a 9" baking pan or skillet holds about 6c.
The more relevant measurement is surface area, a proportion of about 117/63- though the sloped sides of the pie plate throw that off a little.