Waist sizes for pants in the US are deceptive. When I started working with a personal trainer, I was wearing pants with a '34 inch' waist. However, when it came time to take measurements, and I finally relaxed my gut instead of sucking it in so we could get an accurate measurement, my waist measured 38 inches.

Also, one can get 'adjustable waist' pants with elastic slots in them that allow the waist to expand such that someone with a 42 inch waist might fit into a pair of '34 inch' pants comfortably. They don't help the situation any.