MENS NUMBER SIZING NOTE:Size is the chest measurement of the vest itself, NOT your chest measurement. Measure your chest with your shirt or whatever you normally will wear under your vest. Measure your chest and add 2-3 inches to get your vest size. For example, if your chest measures 43 inches, then order a size 46 vest. Measure your belly at the largest part. IF your belly measurement is larger than your chest measurement then order your vest or jacket size based on that. Jackets and vests are about 2 inches smaller in the waist than the chest, so with larger waists you will need to take that into account.