Body Fat Calculator
Uses the US Navy circumference method — a tape measure and four numbers. More informative than BMI, and free.
- Category
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- Fat mass
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- Lean mass
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How the tape method works
The US Navy method estimates body fat from the difference between your waist and neck circumference, adjusted for height. The logic is that neck size tracks frame size while waist size tracks stored fat, so the gap between them is informative. For women the hip measurement is added, since fat distribution differs. It is accurate to roughly ±3–4% against a DEXA scan — considerably better than BMI, considerably worse than a proper scan, and free.
Body fat ranges
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Above average | 25%+ | 32%+ |
Women carry more essential fat than men — it is required for hormonal function, not surplus. Sustained very low body fat in women is associated with menstrual disruption and reduced bone density, which is why the female ranges sit roughly 10 points higher throughout.
Getting consistent measurements
The method is far more useful for tracking change than for a single absolute number, and consistency is what makes tracking work.
- Measure at the same time of day, ideally first thing in the morning before eating.
- Do not pull the tape tight. It should sit flat against the skin without compressing it.
- Breathe out normally and relax your stomach. Holding your breath or bracing invalidates the reading.
- Measure three times and average — a centimetre of tape placement changes the result by about a percentage point.
- Use the same tape each time. Cloth tapes stretch over months.
How the methods compare
| Method | Typical error | Cost |
|---|---|---|
| DEXA scan | ±1–2% | $50–150 per scan |
| Hydrostatic weighing | ±2% | Specialist facility |
| Skinfold calipers, skilled operator | ±3% | Cheap, needs practice |
| US Navy tape method | ±3–4% | Free |
| Bathroom scale (bioimpedance) | ±5–8% | Built into many scales |
| BMI as a fat proxy | Very poor for individuals | Free |
Bioimpedance scales are heavily affected by hydration, which is why the same scale can report a two-point change overnight. If you use one, weigh in under identical conditions every time and watch the trend rather than the number.
How to use the Body Fat Calculator
- Choose your units and enter your height.
- Measure your neck just below the larynx, with the tape sloping slightly downward at the front.
- Measure your waist at the navel, relaxed, after breathing out. Women measure at the narrowest point.
- Women also measure hips at the widest point. Add your weight for fat and lean mass figures.
Frequently asked questions
How accurate is the Navy body fat method?
Roughly ±3–4% compared with a DEXA scan for most people. It is less accurate at the extremes — very lean or very heavy — and most useful for tracking change over time rather than as an absolute figure.
Why does it need my neck measurement?
Neck circumference correlates with frame size and stores relatively little fat, so it acts as a baseline. The difference between waist and neck is what carries the signal.
What is a healthy body fat percentage?
Broadly 14–24% for men and 21–31% for women. Below the essential fat threshold — about 5% for men and 13% for women — is not sustainable or healthy.
Why do women need a hip measurement?
Because women typically store more fat on the hips and thighs, which the waist measurement alone would miss. The female formula accounts for both.
Is this better than BMI?
For estimating body fat, considerably. BMI cannot distinguish muscle from fat at all, whereas the tape method responds directly to where fat is actually stored.
Related tools
Last reviewed September 4, 2026. A tape estimate with roughly ±3–4% error. Not a substitute for a DEXA scan or medical assessment.