A size 40 will work but i would suggest you go with the size 38
No, a size 38 pant will want the size 40 gun belt (some people may want a 42" to have it sit even lower on their hips) - I don't understand how the maker of the gun belt doesn't know/understand how a gun belt is worn. It is not a belt to hold up your pants, it does not sit at the waist, but on the hips; instead - therefore a person's 'pant/waist size' is incorrect. Measure a gun belt for your hips, not your waist.
I bought one recently after talking to Desantis Customer Service. My pant size is 36. I measured with a tape measure where I wanted the belt to sit on my waist. I wanted it to sit right under my pants belt. The measurement I got was 41 inches. I ordered a 42 belt. It was perfect.
If you want it to sit lower like in the western movies then you want it a bit larger. Measure where you want it to fit. Sitting right under your pants belt is actually where a belt like this was worn in the old days. If you look online and read you will see this historical information.
This is what Desantis will say if you contact them. The other people answering dont seem to know what they are talking about.
Bought my waist size and the belt was too small. 2-4" above your waist size would be better.