Restoration of the joint line of the knee during primary and revision total knee arthroplasty is one of many critical steps that directly influence patient outcomes. Fifty MRI scans of normal atraumatic knees were analyzed to determine a quantitative relationship between the joint line of the knee and the bony landmarks of the knee joint: femoral epicondyles, metaphyseal flare of the femur, tibial tubercle, and proximal tibio-femoral joint. We describe the relationship of these six anatomic landmarks about the knee in a gender and size independent manner. This description supports a simple three-step algorithm allowing orthopaedic surgeons to calculate, instead of estimate, the location of the joint line of the knee.