What I do is, measure the client.. Then If I don't have the measurement, I subtract 4 inches from the hip measurement to get the knee circumference, if it's for elderly ones, then 6 to 8 inches from the hip measurement if it's for young ones
To get knee circumference Hip 40 - 4 Inches Knee circumference=36 So 36 inches is the circumference, but this method works for clients that doesn't want something fitted. Or send me a DM 08146642967