For the most accurate measurement, use a soft measuring tape.
To get your top strap measurement, wrap the tape around your leg just above your kneecap, rather than high up on the quad. To get your bottom strap measurement, wrap the tape around your leg just below the kneecap. No need to pull the tape too tightly!
Between two sizes? Go by the above the knee measurement. The top strap is the measurement that matters more.
On the high end of a size range? Size up if you aren't sure.
What’s most important is the strap overlap. You want the loop strap to reach as far across as it can without having extra strap flappage (and that's totally an industry term). About an inch of exposed hook is okay. The overlap is where the strength comes from.
If you find that the top strap pops open, you probably need to size up for longer straps. If this happens, stop wearing your Bee’s Knees, keep them clean, and contact Bee for sizing and exchange info. We are happy to help you find your fit!