How to measure yourself
Use a flexible tape measure, keep it level and snug without squeezing the skin, and measure on bare skin. Taking each measurement two or three times and using the average makes the result more reliable.
- Height: standing straight, without shoes.
- Neck: just below the Adam's apple (larynx), with the tape sloping slightly down toward the front.
- Waist (men): horizontally at the level of the navel (belly button).
- Waist (women): at the narrowest point, usually between the bottom of the ribs and the navel.
- Hips (women): around the widest part of the buttocks.
Breathe out normally and relax your stomach. Don't pull it in.
The U.S. Navy body fat formula
This calculator uses the circumference method developed by the U.S. Naval Health Research Center, which the U.S. military has used for body composition checks. With all measurements in centimetres:
Men: 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
Women: 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450
Imperial measurements are converted to centimetres first (1 inch = 2.54 cm).
Example: a man who is 178 cm tall, with a 38 cm neck and 86 cm waist.
waist − neck = 48. log10(48) = 1.681 and log10(178) = 2.250.
495 ÷ (1.0324 − 0.3207 + 0.3478) − 450 = 17.2% body fat, in the "fitness" range.
Body fat categories
These ranges come from the American Council on Exercise (ACE):
| Category | Women | Men |
|---|---|---|
| Essential fat | 10–13% | 2–5% |
| Athletes | 14–20% | 6–13% |
| Fitness | 21–24% | 14–17% |
| Average | 25–31% | 18–24% |
| Obesity | 32% and above | 25% and above |
Women naturally carry more essential fat than men, for hormonal and reproductive health, so the ranges are higher.
How accurate is it?
Studies comparing the Navy method with lab methods such as DEXA scans generally find it's within about 3–4 percentage points for most people. It's less accurate for very muscular people and for people with a lot of fat stored in one area. Its big advantage is consistency: measuring the same way each month is a good way to track change over time, even if the exact number is a little off.
Good to know: this is an estimate for adults, not a medical test. For an accurate measurement, ask a doctor or clinic about DEXA or bioimpedance testing. You can also compare with your BMI, which uses only height and weight.
Frequently asked questions
Is body fat percentage better than BMI?
It tells you something BMI can't: how much of your weight is fat. Two people with the same BMI can have very different body fat. BMI is still useful as a quick screening number, and the two together give a fuller picture.
Why do I need my weight?
The body fat percentage only needs height and measurements. Your weight is used only to split it into fat mass and lean mass (everything else: muscle, bone, organs and water).
How often should I measure?
Every 2 to 4 weeks is plenty. Measure at the same time of day, ideally in the morning before eating, so daily changes in water and food don't skew the result.
Last reviewed November 2026.