Body fat percentage is the total mass of fat divided by total body mass. It's a better indicator of fitness than body weight alone. The US Navy method uses circumference measurements, while skinfold methods use caliper measurements at specific body sites.
Men: Essential fat 2-5%, Athletes 6-13%, Fitness 14-17%, Average 18-24%, Obese 25%+
Women: Essential fat 10-13%, Athletes 14-20%, Fitness 21-24%, Average 25-31%, Obese 32%+