How the Navy method works
Developed by the Naval Health Research Center, the method predicts body density from circumference measurements, then converts it to body fat percentage:
Women: %BF = 495 ÷ (1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.221·log₁₀(height)) − 450
Measure with a soft tape, snug but not compressing the skin: neck just below the larynx, waist at the navel for men and at the narrowest point for women, hips at the widest point. Take each measurement twice and average.
Body fat category ranges (ACE)
| 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%+ | 32%+ |
How accurate is it?
Studies put the Navy method within ±3–4 percentage points of DEXA scans for most body types — comparable to consumer bioimpedance scales and far more consistent than visual guessing. Its real strength is tracking change: measured the same way at the same time of day, the trend over weeks is very reliable even if the absolute number is slightly off.
This tool provides general estimates for educational purposes and is not medical advice. Consult a healthcare professional for guidance specific to you.
Frequently asked questions
What is a healthy body fat percentage?
General fitness ranges are roughly 14–17% for men and 21–24% for women, with 'average' extending to 24% and 31% respectively. Women naturally carry more essential fat; dropping near essential levels (5% men / 13% women) is neither necessary nor healthy for most people.
Why does my result differ from my smart scale?
Different methods, different errors. Bioimpedance scales are sensitive to hydration, food, and recent exercise and can swing 2–5 points in a day. Pick one method, measure under consistent conditions, and judge the trend rather than comparing devices.
Where exactly do I measure my waist?
For this formula: men at the navel, women at the narrowest visible point. Stand relaxed, exhale normally, keep the tape level, and don't pull it tight enough to dent the skin.
Can I lose fat in one spot only?
No — spot reduction doesn't survive controlled studies. Fat loss location is set by genetics and hormones. A calorie deficit with resistance training reduces overall fat while preserving muscle, and stubborn areas simply lose last.
How fast can I realistically lower body fat?
Sustainable fat loss runs about 0.5–1% of body weight per week. For a 80 kg person that's roughly 1.5–3 percentage points of body fat per month early on, slowing as you lean out.