These reproductions of the U.S. Army enlisted cavalry saber belt will be made by L.D. Haning, and will copy an original example of the early version of the belt made of waxed flesh leather and stitched rather than riveted together.
 
To get the right fit, you need to measure your waist where you wear your belt, in inches.  If you provide your pants size, you're going to get a belt that is far too small.  Take a string, wrap it around yourself, and measure the string.  Or measure a Civil War belt you already wear from the prong on the buckle to the adjustment hole that you use.  The center hole on these belts will be placed at the measurement you provide, so if it doesn't fit that's on you.