When I make one for my wife, if it's going to be tooled I go 1-1/4" wide to have room for the design.
Like this one. The belt is 1-1/4" and the buckle is 1" wide.
Plain belts look better at 1" or 1-1/8", depending on the buckle.
For men, 1-1/2" or 1-5/8".