When storing your leather belt it is recommended that you either hang it from its buckle or curl it up, starting with the buckle and be sure it is not disturbed in a way that can cause it to become misshapen. Most denim belts do not need any more special care. It wouldn't hurt to spray your belt with a high-quality water and stain repellant but it isn't truly necessary.
Dress belts require a little more care that they did not get wrinkled and crack. If you keep dress belts in a drawer be careful that they don't get scuffed or pressed down and misshapen by the other items in the drawer.
Belts are measured using millimeters.
All jeans have loops made for 40 mm belts. Some jeans have loops for 50 mm or wider. Most dress belts are 25-32 mm. There are also some very slim belts that range from 15-20 mm.
To see if your jeans can handle a wider belt measure the belt loop and use the calculator below to determine what belt size you need.