The US Navy circumference method
Developed by the Naval Health Research Center in the 1980s, this method estimates body fat from circumference measurements and height. It was designed to be practical — usable with a tape measure by personnel with no equipment or training — while staying within about 3–4% of hydrostatic weighing for most people.
The formulas (metric)
- waist
- At the navel for men, narrowest point for women
- neck
- Just below the larynx
- hip
- Widest point of the buttocks — women only
The logic is that abdominal circumference relative to neck and height correlates strongly with total body fat. The women's formula adds hip circumference because female fat distribution differs.
Measuring accurately
- Measure first thing in the morning, before eating or drinking.
- Keep the tape snug but not compressing the skin.
- Stand relaxed — do not suck in or flex.
- Take each measurement three times and average them.
- Use the same tape and the same landmarks every time.
What the number means
| Category | Men | Women |
|---|---|---|
| Essential fat | 2% – 5% | 10% – 13% |
| Athletes | 6% – 13% | 14% – 20% |
| Fitness | 14% – 17% | 21% – 24% |
| Average | 18% – 24% | 25% – 31% |
| Obese | 25% and above | 32% and above |
Women require more essential fat than men — it is structurally necessary for hormonal and reproductive function. A woman at 10% body fat is at the physiological floor; a man at 10% is simply lean.
How this compares with other methods
| Method | Typical error | Practicality |
|---|---|---|
| DEXA scan | ±1–2% | Clinical, $100–150 per scan |
| Hydrostatic weighing | ±2–3% | Lab only, requires full submersion |
| Bod Pod | ±2–3% | Specialist facilities |
| Skinfold calipers | ±3–4% | Cheap, but heavily technique-dependent |
| US Navy method | ±3–4% | Tape measure only — this calculator |
| Bioelectrical impedance | ±4–8% | Common in scales; varies with hydration |
The Navy method is least accurate for people at the extremes — very lean, very obese, or very muscular — because the underlying regression was fitted to a broadly typical population. For anyone in the middle range it is remarkably good for the cost.
Body fat percentage is a considerably better health indicator than BMI, because it distinguishes muscle from fat. Compare with the BMI calculator, and use your result in the BMR calculator for a Katch-McArdle metabolic estimate, which is more accurate than Mifflin-St Jeor once body fat is known.
Frequently asked questions
How accurate is the US Navy body fat method?
Within about 3–4% of hydrostatic weighing for most people, which is comparable to skinfold calipers and better than most bioelectrical impedance scales.
Accuracy drops for the very lean, the very obese, and the heavily muscled, since the formula was fitted to a typical population.
What is a healthy body fat percentage?
For men, 14–17% is the fitness range and 18–24% is average. For women, 21–24% is fitness and 25–31% is average.
Women require more essential fat than men for hormonal function, which is why every category sits about 10 points higher.
How do I measure my waist correctly?
Men measure at the navel. Women measure at the narrowest point of the natural waist, usually just above the navel.
Stand relaxed with the tape snug but not compressing the skin, exhale normally, and do not suck in. Measure at the same time of day each time.
Can I lose fat without losing weight?
Yes — this is body recomposition, gaining muscle while losing fat. It is most achievable for beginners, people returning after a break, and those with higher starting body fat.
It is why tracking body fat matters more than the scale. Weight can hold steady while composition improves substantially.
Why is my scale's body fat reading different?
Bioelectrical impedance scales pass a small current through the body and infer composition from resistance. Hydration level, recent food, exercise and even skin temperature shift the reading — swings of several percent within a day are common.
Weigh under identical conditions each time and treat the trend rather than any single reading as the signal.