We don't think you will find better leg protection at this price.
These are one-size-fits-most.
The distance between the top of the opening at the ankle and the center of the knee is 15". If you have a distance below 13" then your foot will push the "knee" above your knee, but it will still work as protection. We do not recommend these if your top-of-foot-to-center-of-knee is less than 12", but very few adults are in that category.
As with everything we sell, you can return these for a full refund of the purchase price if they don't move and feel right for you.