Underwater weighing: The gold standard for body composition analysis, this method determines your percentages by measuring overall body volume and density. It’s used mostly in laboratories and is unpopular with the laity, since most people would rather not be dunked in a tank.
Bioelectrical impedance analysis: A weak current is run through your body, and the conductivity (stymied by fat tissue) is put into and algorithm to determine the ratio of fat to lean mass.
Skin-fold test: Wielding a caliper, a technician pinches hunks of flesh from three to seven locations. While inexpensive and portable, the accuracy of this approach depends on the tester’s skill and experience.
Waist-to-hip ratio: This DIY technique determines if your fat is distributed in healthy proportions: Wrap a tape measure around your waist (at your belly button) and around the widest part of your hips. Divide waist measurement by hip measurement. According to the American Council on Exercise, women whose ratios are greater than 0.8 are at higher risk for hypertension, high blood pressure, stroke and diabetes.