Suits are usually sold as a unit, but they are comprised of two separates, the trousers and the coat (three if there is a vest). The trousers and coats are sized by the waist measurement and the chest measurement, respectively. The trousers of men's suits are usually not hemmed. They will measure your inseam and hem them to the proper length or you can take them to a tailor who will do the same. They can alter the length of the coat sleeves as well.
Paige