With numerous surviving examples, including one worn by a member of Pickett's Division, one of the most frequently encountered Confederate belts with provenance to the Gettysburg Campaign is a particular style of roller buckle belt that was cut wide with a billet and chape that tapers down to fit a 1 1/2" wide black-enameled cast iron roller buckle.  While each varies slightly, to include being made from both bridle leather and waxed flesh leather, the similarities indicate a large number of this general type of belt were present in the ANV in the middle part of the war.
 
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.