You have to take a measurement to determine what length your new belt will be. whether your old belt is a bit too long, or a bit too short, take a measurement from the hole that you're using now to the tip of the buckle. This measurement lets me calculate the correct length of the new belt. You can take this measurement in centimetres or inches as you will be typing this figure in later. Do not go by the number on the back of your old belt, manufacturers sizes vary. Even waist sizes on jeans or trousers can be inaccurate. The best way to measure for your new belt is to measure your old belt. Remember, measure from the hole that you use now to the tip of the buckle. (Not sure? See photos.)

How to measure for a complete belt.