Find your body fat percentage with just a tape measure, using the US Navy circumference method (Hodgdon & Beckett, 1984) — validated against hydrostatic weighing with about a 3-4% margin of error.
Body fat % and lean body mass are two sides of the same coin. Check your fat-free mass with our dedicated calculator.
Calculate My Lean Body Mass 🚀| Category | Men | Women |
|---|---|---|
| Essential Fat | 2-5% | 10-13% |
| Athletic | 6-13% | 14-20% |
| Fitness | 14-17% | 21-24% |
| Average | 18-24% | 25-31% |
| Obese | 25%+ | 32%+ |
Source: American Council on Exercise (ACE) body fat percentage categories.
Bioelectrical impedance scales (the kind most people have at home) estimate body fat by sending a small electrical current through your body — but that reading shifts significantly based on hydration level, what you ate, and even the time of day, sometimes swinging several percentage points within the same day. The Navy circumference method uses fixed physical measurements that don't fluctuate with hydration the same way, which is part of why it remains in active use for military fitness standards decades after it was developed.
This method was developed and validated on a military population, so its accuracy can drift slightly for body types far outside that reference group — very muscular athletes, for example, sometimes get a higher estimate than their actual fat percentage, since the formula can't distinguish a large waist from muscle versus fat. Use it to track your own trend over time rather than treating any single reading as an exact lab measurement.
Validated against hydrostatic (underwater) weighing, the gold-standard lab method, the Navy circumference formula has a margin of error of roughly 3-4 percentage points for most people. That's notably better than most home bioelectrical impedance scales.
First thing in the morning, before eating or drinking, gives the most consistent reading. Measuring at different times of day can shift your waist circumference by half an inch or more just from food and water in your system.
Skinfold calipers and the Navy circumference method measure different things (subcutaneous fat thickness at specific sites vs. overall circumference), so some difference is expected. Both are estimates — pick one method and stay consistent with it so your trend over time is meaningful.
See our full comparison of DEXA, BIA scales, calipers, and the Navy method by accuracy, cost, and convenience. In the U.S. Army? The Army Body Fat Calculator uses the official 2023 one-site tape method and AR 600-9 standards.