Body Fat Calculator
Estimate your body fat percentage using the US Navy circumference method. Enter your sex, height, and neck, waist (and hip for women) measurements.
How it works
The US Navy method estimates body density from body circumferences and height, then converts it to a body fat percentage. Measurements are entered in centimeters and converted to inches internally.
US Navy circumference formula (log₁₀-based)Worked examples
Male: 175 cm tall, 38 cm neck, 90 cm waist
An estimated body fat of 20.7%, in the average band. Measuring the neck and waist accurately matters more than anything else here: a single centimetre out moves the answer by about a percentage point.
Female: 165 cm tall, 32 cm neck, 75 cm waist, 95 cm hips
An estimated body fat of 27.4% by the same method. The female formula asks for hips as well, because the measurement points differ by sex.
When the neck and waist measurements match
The formula takes the logarithm of the difference between the waist and the neck, so if the two measurements come out the same the calculation has nothing to work with. A reading like that almost always means one of the measurements is wrong, most often a neck measured around the collar rather than at its narrowest point.
What this assumes, and where it does not apply
What it assumes
- The US Navy circumference method: neck, waist and (for women) hip measurements combined with height.
- Measurements are taken with a tape at the points the method specifies, at the widest or narrowest point as appropriate.
- The formula is applied to the measurements exactly as entered, so it cannot detect a tape that slipped or a reading taken at the wrong point on the body.
Where the result does not apply
- An estimate from tape measurements, not a measurement of body fat: it typically lands within a few percentage points of a DEXA or hydrostatic result.
- Less reliable at very high or very low body fat, and for children, pregnant women and highly muscular people.
- It cannot track a change over a few weeks, because the estimate moves by less than the ordinary measurement error of a tape and a real change is indistinguishable from a re-measurement difference.
Frequently asked questions
How accurate is the US Navy method?
It is a reasonable estimate (±3–5%) but not as precise as DEXA or hydrostatic weighing.
What is a healthy body fat percentage?
For men, roughly 14–24% is average; for women, roughly 21–31%.
Why do women need a hip measurement?
The female formula includes hip circumference because women store fat differently.
Where exactly should I measure my waist?
At its narrowest point, with the tape level and snug but not compressing the skin. Measure the neck in the same way at its narrowest point, and take each reading the same way every time, because consistency matters more than any single measurement.
This tool is for general information only and is not medical advice. Always consult a qualified healthcare professional before making health-related decisions.
Delta Tech Solutions prepared this page. No doctor, nurse or other qualified health professional reviewed it, and it is not medical advice — talk to a qualified healthcare professional about your own situation.
Maintained by David M at Delta Tech Solutions · Figures last checked 10 October 2026 · Next check due 10 April 2027
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