What body fat percentage is
Your body fat percentage is the share of your total weight made up of fat, as opposed to lean mass: muscle, bone, water and organs. It tells you far more than the number on the scale. Two people can weigh exactly the same yet look and perform completely differently, because one carries more muscle and the other more fat. Body fat percentage captures that difference; body weight alone hides it.
This calculator uses the US Navy method, a formula the United States Navy developed to estimate body fat with nothing more than a tape measure. Everything runs in your browser, and your measurements are never stored or sent to a server.
How to use the calculator
- Pick your sex — the formula differs for men and women.
- Enter your height in centimetres.
- Measure your neck just below the larynx, letting the tape slope slightly downward at the front.
- Measure your waist: at the navel for men, at the narrowest point of the abdomen for women.
- If you are female, add your hip measurement at its widest point.
Measure against bare skin or very thin clothing, keep the tape snug but not tight, and take each reading at the end of a normal breath out. Measure two or three times and average the results — a single centimetre at the waist noticeably shifts the estimate.
The US Navy method
For men the formula is:
body fat % = 495 / (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
For women the hip measurement is added:
body fat % = 495 / (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450
All measurements are in centimetres and log10 is the base-10 logarithm.
Worked example
A man who is 180 cm tall, with a 40 cm neck and a 90 cm waist:
- waist − neck = 50; log10(50) = 1.69897
- log10(180) = 2.25527
- Denominator = 1.0324 − 0.19077 × 1.69897 + 0.15456 × 2.25527 = 1.05682
- 495 / 1.05682 − 450 = 18.4 %
At 18.4 %, he lands in the “acceptable” range for men.
Reference ranges by sex
Common ranges from the American Council on Exercise (ACE):
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5 % | 10–13 % |
| Athlete | 6–13 % | 14–20 % |
| Fitness | 14–17 % | 21–24 % |
| Acceptable | 18–24 % | 25–31 % |
| Obesity | 25 % or more | 32 % or more |
Women naturally carry more essential fat for hormonal and reproductive reasons, which is why their healthy ranges sit higher than men’s.
Body fat versus BMI
BMI only compares weight to height, so it labels many muscular people as “overweight” and misses hidden fat in slim people who sit at a normal weight. Body fat percentage looks at what your weight is actually made of, so it complements BMI rather than replacing it.
Frequently asked questions
What body fat percentage is healthy?
For most adults, roughly 10–20 % for men and 18–28 % for women is considered healthy. Dropping below essential fat (about 5 % for men and 13 % for women) starts to carry real health risks.
Is this more reliable than a bioimpedance scale?
They work differently. A bioimpedance scale passes a small electric current through the body, and its reading swings with hydration, your last meal and recent exercise. The Navy method depends on measuring accurately with the tape. Both are estimates; for the highest accuracy, a DEXA scan is the reference standard.
How do I measure neck and waist correctly?
Measure the neck just below the Adam’s apple with the tape angled slightly downward. Measure the waist with your abdomen relaxed at the end of a breath out — no sucking in, no cinching the tape. Always measure at the same time of day and under the same conditions so you can track changes fairly over time.