Depending on the type of orthopedic knee support that you need, you might have to measure different parameters. To ensure accurate measurements, use a soft, flexible measuring tape and ask someone else to do it for you. The most common measure for knee braces is knee circumference, which is right over the middle of your knee. If a knee brace sizing chart mentions thigh circumference or calf circumference, measure these six inches up and down from the middle of the knee. Make sure your leg is well extended during measurements.