Sharing a divide with Mazda's 6 IF you want to know the difference between a small SUV and a medium SUV, multiply the length of the vehicle by its width. The categories are split by footprint. Above a certain size, it's medium. Of course, you don't need to know. You just need to find one that suits you. It does help to build a shopping list, though, and for the industry some sort of scheme is essential. Most commonly used is a system based on letters. A "C-segment" car means the Toyota Corolla and its rivals. B is smaller, D is larger, and so on.