How to Properly Measure a Belt
Proper measurement of your belt is important. The overall length of the strap has no bearing on the size of the belt that you need. DO NOT rely on any number printed on a belt that you currently own from another manufacturer as they are not all consistent in their sizing.
Lay a belt that you currently own on a flat surface and measure the distance from the "Pin" or "Prong" where it intersects with the upper inside of the buckle, down the 3rd or middle hole towards the opposite end. Or, measure to the "Current" hole that you are using. This distance is the size that you will need to fit properly.
Be sure to take into account "Where" you are going to wear this belt. Will it be on your Waist or down on your "Hip"? It is rare that one size belt will work for both.