How to use
- Choose your sex and units, then enter your age, height and weight.
- Measure your neck and abdomen (men) or waist (women) with a soft tape. Women also need their hips.
- The US Navy result is shown large, with the BMI-based estimate, fat mass, lean mass and the category table for your sex.
This calculator provides general information only and is not medical advice.
Where to measure
These follow the US Department of Defense body composition procedure. Keep the tape level and snug without compressing the skin, and average two or three readings.
| Site | Men | Women |
|---|---|---|
| Neck | Just below the larynx | Just below the larynx |
| Abdomen / waist | Level with the navel, after a relaxed breath out | At the narrowest point of the waist |
| Hips | — | At the widest point of the buttocks |
Formulas
US Navy circumference method (Hodgdon & Beckett, 1984, Naval Health Research Center), with measurements in cm and log base 10:
| Sex | Body fat (%) |
|---|---|
| Men | 495 ÷ (1.0324 − 0.19077 × log(abdomen − neck) + 0.15456 × log(height)) − 450 |
| Women | 495 ÷ (1.29579 − 0.35004 × log(waist + hip − neck) + 0.22100 × log(height)) − 450 |
Inch measurements are converted to cm first, so switching units does not change the result. (The DoD’s inch-based version of the equation agrees to within about half a percentage point.)
Deurenberg formula (Deurenberg et al., British Journal of Nutrition, 1991) for adults: body fat % = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4, where sex = 1 for men and 0 for women.
Categories (American Council on Exercise)
| 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% and above | 32% and above |
Examples
- Man, 30, 5 ft 10 in, 170 lb, neck 15 in, abdomen 34 in → 17.4% (fitness), about 29.6 lb of fat. His BMI is 24.4, and the Deurenberg estimate is 20.0% (average).
- Woman, 163 cm (5 ft 4 in), neck 32 cm, waist 72 cm, hips 96 cm → 26.9% (average).
It is normal for the two methods to disagree: the tape method reflects your actual shape, while Deurenberg reflects the average link between BMI, age and fat.
Things to keep in mind
- Moving the tape a centimetre or two changes the result. Measure at the same time of day, the same way, if you want to track change.
- Both methods are estimates and can differ from DEXA or underwater weighing by several percentage points — and from bioimpedance scales too.
- Deurenberg is for adults and overestimates fat in very muscular people.
- Body fat percentage is not a diagnosis. Talk to a health professional about your weight and metabolic health.
FAQ
Should I look at body fat or BMI?
Both. BMI is easy to measure but cannot tell muscle from fat; body fat shows composition but carries more measurement error. Check BMI with the BMI calculator.
I got “below essential fat”. What now?
Usually a measurement landed in the wrong place or the units were mixed up. If your body fat really is that low, it can affect hormones and immunity — see a doctor.
What can I do with my body fat percentage?
It gives you lean body mass, which you can plug into the Katch-McArdle equation in the BMR calculator for a more personal estimate.