OD POD: A method for determining the lean body mass. The BOD POD is a computerized, egg-shaped chamber. Using the same whole-body measurement principle as underwater weighing, the BOD POD measures a subject's mass and volume, from which their whole-body density is determined. Using these data, body fat and lean muscle mass can then be calculated.
Assuming a skilled technician and cooperation of the subject, the best way to measure body fat is hydrostatic underwater weighing. Nearly as good and less expensive is DEXA (duel energy X-ray absorptiometry). The least expensive is air displacement (BodPod) and it is nearly as good as underwater weighing. As a practical matter at home, using plastic skinfold calipers may be all you need. They involve a one-time expense of $20. .
You can't just figure it. Body fat needs to be measured before and after weight lossto determine the percentage lost. Skin calipers, bioelectrical impedance, bodpod,X-rays or MRI can be used to determine this.