Do not GUESS on measuring for a kilt. Once you measure, DO NOT add sizes to your measurement. Order the size you measure. That way you know you will get the right one to fit you.
Standard and Deluxe Utility Kilts: Order the size measured or order one size up if you are in between sizes.
Wild Outdoor/Wilderness Utility Kilts: Order the size measured. If you are in between, you can order the size down or up since the Velcro waist is adjustable.
Ultimate Utility Kilts: Order the size measured. If you are in between, you will want to order the size down (37 waist would go down to 36)
Traditional Tartan Kilts: The size stated on each kilt is the smallest setting on the buckle straps (a size 36 adjusts from a 36 up to just under a 40). Depending on where you want the buckle to end on your waist will determine your size. A good rule of thumb to follow is to go down 2 inches from your measured waist size. That will put you in the middle of the buckle straps (i.e. 40 measured would order a 38)
How to measure for a kilt with out measuring the waist.
Use this when giving a gift or other situation where you are not able to measure their waist.
When you are measuring a pair of pants to determine sizing, it should be around 3-4 inches bigger than what the jeans size says (some sizes closer to 30 are only 2 inches bigger). You should only use this option as a last resort if personally measuring the person is not possible. DO NOT USE THIS OPTION IF YOU CAN MEASURE YOURSELF. Save yourself the time and just do it right the first time!
If for some reason you are just not able to measure anything, you can make a good guess at which size they would need. I would go up two sizes if guessing, i.e. 40 will go to a 44 size kilt. This is only a guess and does not replace at least trying to measure if possible.