El Paso Saddlery makes some beautiful gun belts...pricey but A#1, first quality.
I've made up a dozen or so for family and friends over the years so the dimensions I use are what we wear. For jeans, 1-1/2" is about all you can get through the belt loops. Other trousers, you'd better measure. The wider the better if you carry.
I make mine up from single thickness, bull hide leather I buy from a local saddle maker. It's skirting leather and almost 1/4" in thickness...that eliminates sag, even with a full size, all steel duty gun.
By far the most comfortable gun belt I've ever worn is one I made up to copy the rough-out, money/gun belt John Wayne wore in many of his westerns. Mine's 2-1/4" wide and without the loops that The Duke wore. I also made up a cpl slide on cartridge carriers in several calibers to use with it.
Over time it molds to your body like a well worn pair of Levis, yet supports the gun nicely. For the really big revolvers, Colt or Ruger, nothing works as well. The width precludes using it as a trouser belt, but for gun work, it's tops. Here's a cpl pics. (El Paso Saddlery makes up some that are similar)
HTH's, Rod