The size of the riding mower that you need will depend on how large your yard or cutting area is. If you have a large cutting area, then a larger, more powerful riding mower will be needed as they will complete a whole cut of your lawn in one go as opposed to needing to stop halfway through to refill the tank. The best riding mowers will show the total cutting area from one fuel tank or charge, so make sure you know the size of your yard before purchasing.