Garbage disposal size is determined by the horsepower rating. When deciding how to choose a garbage disposal, consider the foods you'll be disposing, the volume you'll be disposing, and compare that to the horsepower rating of your unit. If you're doing limited service and just grinding up fruits and vegetables, you can probably get away with something in the 1 hp or less range. If you're a cafeteria that needs to dispose lots of meats, you're going to be in the 5+ hp range. Most full service restaurants fall somewhere in the middle.