How to measure correctly
Accuracy depends almost entirely on measuring consistently. Use a flexible tape, keep it snug but not compressing the skin, and measure at the same time of day.
- Neck — just below the larynx, tape sloping slightly downward at the front.
- Waist — at the navel for men; at the narrowest point for women. Measure after a normal exhale, without pulling the stomach in.
- Hips (women only) — at the widest point of the buttocks.
- Height — without shoes.
The formula and how the maths works
The US Navy method uses logarithmic circumference equations:
Men: %BF = 495 ÷ [1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)] − 450
Women: %BF = 495 ÷ [1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)] − 450
All measurements in centimetres. The method works because fat distributes in fairly predictable patterns relative to frame size — which is also why it's less reliable for people at the extremes of body composition.
Reference ranges
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Acceptable | 18–24% | 25–31% |
| Above range | 25%+ | 32%+ |
Women naturally carry more essential fat than men — this is normal physiology, not a difference in fitness. Comparing a woman's percentage against male ranges is a common and misleading error.
Worked example
A man, 175 cm tall, neck 38 cm, waist 88 cm:
| Step | Value |
|---|---|
| Waist − neck | 50 cm |
| log₁₀(50) | 1.699 |
| log₁₀(175) | 2.243 |
| Body fat | ≈ 20.6% |
That falls in the "acceptable" band. If his waist came down to 82 cm at the same height and neck, the figure would be roughly 17% — in the fitness range.
Body fat vs BMI
BMI uses only height and weight, so it can't distinguish muscle from fat. A muscular 85 kg athlete at 178 cm has a BMI of 26.8 — technically "overweight" — while carrying perhaps 12% body fat.
Body fat percentage is more informative for that reason, but the tape method is less precise than BMI is at what it measures. In practice:
- Use BMI for a quick population-level screen. See our BMI calculator.
- Use body fat percentage to track composition changes while training.
- Use waist circumference alone as a simple health marker — above 90 cm for men and 80 cm for women of South Asian descent is associated with increased metabolic risk.
The most useful signal is often the direction of travel rather than any single figure.
Accuracy and limits
- Typical error is around ±3–4 percentage points against a DEXA scan.
- Least accurate at the extremes — very lean or very high body fat.
- Doesn't distinguish subcutaneous from visceral fat, though waist size is a reasonable proxy for the latter.
- Hydration, meals and time of day all shift measurements slightly.
For tracking progress, consistency beats precision. Measure the same way, at the same time, every two to four weeks. A number that moves steadily in one direction is meaningful even if its absolute accuracy is imperfect.
If you have concerns about your weight or body composition, a doctor or registered dietitian can give you guidance based on your full health picture rather than a formula.
Frequently Asked Questions
How accurate is the US Navy method?
Typically within about 3–4 percentage points of a DEXA scan for most people. It's least reliable at very low or very high body fat levels.
What is a healthy body fat percentage?
Broadly 14–24% for men and 21–31% for women, with athletes often lower. These are population guides rather than individual targets.
Why do women have higher body fat?
Essential fat requirements are higher in women for hormonal and reproductive function — around 10–13% compared with 2–5% in men. It's normal physiology.
Can body fat percentage be too low?
Yes. Below essential thresholds it disrupts hormone production, bone density and immune function in both men and women. Very low levels are not healthier.
How often should I measure?
Every two to four weeks is enough. Measuring more often mostly captures noise from hydration and food rather than real change.
Is body fat percentage better than BMI?
It's more informative about composition, but the tape method is less precise. Using both, alongside waist circumference, gives a fuller picture than either alone.
Why did my body fat go up when I gained muscle?
If waist measurement is unchanged but weight rose, the formula may not reflect it — the Navy method reads circumferences, not weight. Track waist size and strength alongside the percentage.
Does the method work for very muscular people?
Less well. Athletes with large necks or narrow waists can get results that understate or overstate actual body fat. Skinfold calipers or DEXA are more suitable there.
Related calculators and guides
Health disclaimer. This calculator provides general estimates for healthy adults and is not medical advice. It cannot account for your individual health conditions, medications or circumstances. Please speak to a doctor or a registered dietitian before making significant changes to your diet, exercise or fluid intake — particularly if you have any medical condition, are pregnant or breastfeeding, or have any history of disordered eating.