Great question, thank you. First for men, belt and waist sizes are two different things. Usually, a man will wear one to two sizes larger for belt. So, someone with a 36x waist will wear a 38 - 40 size belt. Most luxury men's belts are in centimeters. A size 100 is about a 40 and will fit someone with a 36' - 38' waist. Thankfully, the websites usually have conversion tables.