Body Fat Calculator
Estimate body fat percentage using the US Navy tape-measure method.
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This calculator estimates what share of your body weight is fat using the US Navy circumference method, which needs nothing more than a tape measure and your height. Men enter height, neck and waist in centimetres; women also enter a hip measurement. You get a body fat percentage to one decimal place and a category label.
The US Navy equations it uses
The method comes from equations published by Hodgdon and Beckett at the US Naval Health Research Center in 1984, created so the Navy could screen personnel without lab equipment. In their metric form they are:
Men: %BF = 495 / (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450 Women: %BF = 495 / (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450
The part inside the brackets predicts body density from your girths; the outer "495 ÷ density − 450" step is the Siri equation, which converts density into a fat percentage. The hip field is only used in the women's equation, so men can leave it empty.
Worked examples
- A man who is 175 cm tall with a 38 cm neck and 85 cm waist gets 16.9%, labelled "Average".
- If his waist comes down to 80 cm with the same neck and height, the estimate drops to 12.9% ("Fitness"). Five centimetres of waist moves the result by four points, which shows how much careful measuring matters.
- A woman who is 162 cm tall with a 32 cm neck, 76 cm waist and 98 cm hips gets 30.3%, labelled "High".
Measuring correctly
- Neck: just below the Adam's apple, with the tape sloping slightly down towards the front.
- Waist (men): horizontally at the navel, standing relaxed, at the end of a normal breath out.
- Waist (women): the tool's hint says the navel, while the original Navy protocol uses the narrowest part of the torso. Pick one and use the same spot every time.
- Hips (women): around the widest part of the buttocks, feet together.
Keep the tape snug on bare skin without pressing in, take each reading twice and use the average. Inches convert to centimetres by multiplying by 2.54.
What the category label means here
| Label | Men | Women |
|---|---|---|
| Essential / Athlete | under 6% | under 14% |
| Fitness | 6 to under 14% | 14 to under 21% |
| Average | 14 to under 18% | 21 to under 25% |
| High | 18% and above | 25% and above |
These bands are stricter than the widely used American Council on Exercise chart, which treats 18–24% for men and 25–31% for women as average and only starts the obese range at 25% and 32%. A "High" label on this page is therefore not a diagnosis of obesity.
Limits of a tape-measure estimate
Because neck girth is subtracted, a thick, muscular neck pulls the estimate down, and people who store fat mainly on the thighs are not well described by the formula. DEXA scans and hydrostatic weighing are far more precise. The real strength of the Navy method is repeatability: measure every two to four weeks and watch the trend, alongside your BMI and a sensible calorie target. Treat every figure as an estimate for general guidance, not a medical assessment.