The US Navy body fat formula
The US Navy method, developed by the US Naval Health Research Center, estimates body fat from circumference measurements and height. It needs only a flexible tape measure. All measurements go into the formula in centimetres; inches are converted first (× 2.54).
Worked example: man
Height 178 cm, neck 38 cm, waist 86 cm, weight 80 kg.
- waist − neck = 86 − 38 = 48. log10(48) = 1.68124 and log10(178) = 2.25042.
- Denominator = 1.0324 − 0.19077 × 1.68124 + 0.15456 × 2.25042 = 1.05949.
- 495 ÷ 1.05949 = 467.20, and 467.20 − 450 = 17.2% body fat: the "fitness" category for men.
- Fat mass = 80 × 0.172 = 13.8 kg; lean mass = 80 − 13.8 = 66.2 kg.
Worked example: woman
Height 165 cm, neck 33 cm, waist 72 cm, hip 98 cm, weight 60 kg. waist + hip − neck = 137. log10(137) = 2.13672 and log10(165) = 2.21748. Denominator = 1.29579 − 0.35004 × 2.13672 + 0.22100 × 2.21748 = 1.03792. 495 ÷ 1.03792 − 450 = 26.9% body fat, which is "average" for women. Fat mass is 16.2 kg and lean mass 43.8 kg.
ACE body fat categories
The American Council on Exercise (ACE) publishes this widely used chart. The calculator rounds your result to one decimal place and treats values between the published bands (such as 13.5% for a man) as part of the higher band.
| Category | Women | Men |
|---|---|---|
| Essential fat | 10–13% | 2–5% |
| Athletes | 14–20% | 6–13% |
| Fitness | 21–24% | 14–17% |
| Average | 25–31% | 18–24% |
| Obese | 32% and above | 25% and above |
Essential fat is the minimum the body needs for normal function. Women need more than men, for hormonal and reproductive health. Going below the essential range is a health risk.
How to measure each site
- Height: without shoes, standing straight against a wall.
- Neck: just below the larynx (Adam's apple), with the tape sloping slightly down towards the front. Keep your head level and don't flare your neck.
- Waist (men): horizontally at the level of the navel.
- Waist (women): at the narrowest point, usually between the navel and the bottom of the breastbone.
- Hip (women): around the widest part of the buttocks, with feet together.
Use a flexible tape that does not stretch. Keep it level and snug, but not pressing into the skin. Measure on bare skin after breathing out normally, not while pulling the stomach in. Take each measurement two or three times and use the average, since a 1 cm error at the waist moves the result by roughly half to one percentage point.
How accurate is it?
The Navy method is an estimate from body shape. It is quick, cheap and repeatable, which makes it good for tracking change over time with the same tape and technique. It can be less accurate for very lean or very muscular people and for people who carry fat in an unusual pattern. Methods such as DEXA scans are more precise but cost money and need special equipment.
For a simple weight-for-height measure, see the BMI calculator. To plan daily calories, use the calorie calculator.
This calculator gives general information only. It is not medical advice. Talk to a doctor or registered dietitian about your weight and health.
Frequently asked questions
How do I calculate body fat with a tape measure?
What is a healthy body fat percentage?
Why do women need hip measurements?
How accurate is the US Navy method?
What is lean body mass?
Last updated . How we check our tools. Sources: US Naval Health Research Center (1984); American Council on Exercise body fat chart.