Measure around thigh, at the crotch, over your pants. We recommend adding 2" to that measurement. You do not want the chaps to fit tight or you will be squeezed in all the wrong places!
Inseam: (second number in size chart)
Measure from the crotch to the ankle bone. Stop at the ankle bone. Do not measure further because the chaps need to "hang" not fold on the top of your shoes. Generally, the inseam length is 2" shorter than your normal pant inseam length and you can use the EZ Measure way listed below, just measure from the crotch to your ankle bone (don't add anything extra to the length).
If you do not have a tailor's cloth tape measure, measuring is easy: open wallet, remove any denomination bill ($1, $5, $20...doesn't matter). A dollar bill is 6" long. Place the bill around the widest part of your thigh over your pants and measure your thigh end to end using dollar bill, then add 2".
If the dollar bill, end to end, goes around your thigh 4 times, that's 24", you would then add 2", making your chap thigh size a 26"...that's the size you would order.
Why do we want you to wear your chaps 2" shorter than your pants? Because we care! 99.9% of the population wear their pants too long and it bunches on the top of the shoe. That's fine for blue jeans, but, briarproof material is thick and doesn't 'bunch' so if you get them as long as your jeans, instead of bunching, they're going to drag OR the kick-out on your boot will catch the back hem and tear out the hem or bust the zipper track when you step forward. Trust us...we do this for a living...order them 2" shorter. If you wear an odd numbered length of jean, order the next shortest even size. So, if you wear a 31" jean, order 28" long chaps. You will thank us every time you come home and your hem and zipper are still intact. You're welcome!