There are two important measurements regarding knee sleeve sizing. First, you’ll want to figure out how long the sleeves are and if you like the length of them. That’s pretty straightforward — simply measure from the top of where you’d wear the sleeves and see where a particular pair would end up based on their length.
The second measurement is crucial to get right, and it’s the circumference of your knee. You want to measure with a tailor’s tape measure or string around the middle of your knee with a slight bend. Assuming you want knee sleeves with a bit of compression and support, select the size that’s just below that measurement. For example, if you measure 15 inches and the sizes say 13-15 inches and 15-17 inches, order the smaller pair for extra compression.