Hope someone can give some good advice. I am about to start baking for an organization and need advice on converting baking times, almost all of the baking needs to be done in 13x18 pans. Most of my recipes are for 9x13 so am going to try doubling the amounts for a 13x18 but am not sure how much to adjust the baking times. For 8x8 recipes I am going to try tripling the ingredients. Most of the recipes are for cakes, brownies, bars, and fruit crisps. Anyone have experience in doing this?

AI don't know how exactly to work out baking times over and above trial and error but calculating the volume of your pans shows you are right to exactly double your 9x13 recipes to fill 18x13 pand and the 18x13 pans are 3.65times bigger than the 8x8 pans.