Circumference around the lower thigh. If over 5’4″, we suggest looking at adult sizes due to height.
With the knee bent at a 90 degree angle (ex: when sitting down), measure the distance between the upper thigh (crotch) to the middle of the knee cap. At the half way point (middle of that measurement), measure the circumference of the thigh.
**Note: the bottom of the knee pads are a 1/2″ smaller in circumference