Your crotch length! Taking this measurement can cause a lot of grief in getting your pants to fit you properly. Of course, taking this measurement accurately should be easy enough to do, or at least one would think. Just tie a strip of fabric around your waist (that identifies your waist level) then measure from center front around and through your crotch up to center back. Allow for some sitting ease…and you’re done. The Sure-Fit Designs Pants Kit instructions tell you how to then take this measurement and divide appropriately so that you end up with a back crotch length that is 2” longer than your front crotch length. For many body shapes, this technique works perfectly.
For some, you know from experience that you can use a plumb line where the plumb hangs down between your legs and then you measure only what you need in the front, and only what you need in the back body.
CAUTION! Getting that plumb line to hang exactly where your inseam should be is the issue, particularly when doing this yourself. Your posture and where you hold the tape will dramatically affect accuracy. It’s important to have a measuring buddy help you with an accurate reading. It’s a good idea to do this measurement 2 or 3 times and see if you always come up with the same measurements. I recommend using the measuring technique only if you know you are substantially longer than 2” different between front to back crotch lengths.
Here are 2 videos showing you were you need to measure for accurate pants fit and how to then create the front and back crotch length measurements for your body. Take a few minutes to watch and learn.