Body Fat Calculator
Estimate your body fat percentage with the US Navy tape method from your height, neck, waist and (for women) hip measurements, plus fat mass.
Reviewed by Dany, RightSums team · Updated
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health · Daily life · UK & US
Measure your neck, waist and height, plus your hips if you are a woman, and enter them in centimetres or inches. The calculator uses the US Navy circumference equations by Hodgdon and Beckett, which the US Department of Defense set for all services in 2002. Add your weight to see your fat mass and lean mass, then pass the result to the FFMI calculator. It follows the Navy's measuring guide, such as measuring a man's waist across the belly button after a normal breath out. A 2022 study of US Marines found the formula read about 2.6 points low for men, compared with a DXA scan. It is an estimate, not a diagnosis or medical advice.
Accepted inputs
- Sex
- Height (cm, or feet and inches)
- Neck circumference
- Waist circumference (men at the belly button, women at the narrowest point)
- Hip circumference (women)
- Weight (optional, for fat and lean mass)
Outputs
- Estimated body fat percentage
- Fat mass and lean mass
- Circumference value used in the formula
- Step-by-step measuring guide from the US Navy
- Link to the FFMI calculator with your result filled in
How to use the Body Fat Calculator
- Choose metric or imperial units, pick your sex and enter your height, then your neck and waist measurements, plus your hips if you are a woman.
- The calculator converts centimetres to inches and works out a circumference value: waist minus neck for men, or waist plus hips minus neck for women.
- It puts that value and your height into the US Navy equation for your sex to estimate your body fat percentage.
- If you add your weight, it splits it into fat mass and lean mass and offers a link to the FFMI calculator with your figures filled in.
Frequently asked questions
How do I calculate body fat with the Navy method?
For men, the equation in inches is 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76. A man 70 in tall with a 15 in neck and 34 in waist gets 17.5%. In metric, 178 cm tall with a 38 cm neck and 90 cm waist gives 20.3%, or 16.2 kg of fat at 80 kg.
What is the Navy body fat formula for women?
Women use 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387, with everything in inches. A woman 165 cm tall with a 33 cm neck, 75 cm waist and 100 cm hips gets 29.7%. At 65 kg that is 19.3 kg of fat and 45.7 kg of lean mass.
Where do I measure my waist for the body fat calculator?
Men measure across the belly button, arms by their sides, at the end of a normal breath out. Women measure at the narrowest point, usually halfway between the belly button and the bottom of the breastbone. Measure twice; if the two differ by more than 1 inch (2.5 cm), measure again and average the closest two.
How accurate is the Navy body fat calculator?
It is a rough estimate. In a 2022 study of US Marines, it read about 2.6 points lower than a DXA scan for men and 1 to 2 points higher for women on average, with individual differences of around 4 points. Small measuring errors matter too: for a man of 178 cm with a 90 cm waist, 1 cm more adds about 0.7 points.
Is this the same as the Army body fat calculator?
It uses the equations the US Department of Defense set for all services in 2002, which the Army used before it moved to a new method under Army Directive 2023-11. This calculator does not use the newer Army method. For official military results, use your service's own assessment.
Sources
The rates and rules in this tool come from:
- NHS: Calculate your body mass index (BMI) for adults
- NHS: Overweight and obesity in adults
- NHS inform: Obesity
- NHS: Malnutrition
- NHS: Calculate body mass index (BMI) for children and teenagers
- NIH: US Army Accession and Retention Standards: Impact on Obesity and Medical Readiness - PMC
- NIH: Circumference-Based Predictions of Body Fat Revisited: Preliminary Results From a US…
- NIH: Body composition changes during 8 weeks of military training are not accurately…
- US government: Body%20Composition%20Assessment%20(BCA)%202016 (PDF)
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