Inseam: The inseam is the distance from the middle of the crotch seam (right between your legs) to the bottom of the pant leg. You take this measurement on the inside of the pant leg. Lay them out flat, folded in half, to get the most accurate measurement.
Once again, to determine which inseam length you want, it’s best to measure a pair of jeans you like. And you may want a few different options, depending on what shoes you are wearing or what style you’re going for. I keep several different lengths in my closet.
MOTHER Weekender Flare (29) // Evereve James Pullover (S) // Birks (39)
Leg Opening: This is simply the width of the bottom of the hem of the jeans, but before it’s sewn together.
To measure the leg opening, lay the bottom cuff flat and measure from one seam to the other. Then take that measurement and double it. For example, most skinny jeans have a 10″ leg opening, and when you lay them flat, they will measure 5″ across at the hem.
The knee measurement is sometimes listed, but it isn’t important unless you’re comparing flare or bootcut jeans, and then it’s nice to have so you can compare it to the leg opening.