Navy body fat calculator
Estimate body-fat percentage from a tape measure using the US Navy formula — height, neck and waist, plus hip for women.
Tape-measure estimate from the US Navy formula; not a substitute for a DEXA scan.
How this calculator works
The US Navy method estimates body fat from circumference measurements. It was developed as a practical field alternative to hydrostatic weighing for the military, where tape measures are available but laboratory equipment is not. For men the formula uses neck and waist; for women it adds hip circumference. The idea is that fat distribution changes the shape of the body, and those tape measurements capture the change well enough to estimate fat percentage.
Accuracy is typically within 3–4 percentage points for a careful measurement — close enough to track progress, not precise enough to compare with a DEXA scan. Measure at the same time of day, with the tape snug but not compressing the skin, after breathing out normally. Waist is measured at the navel for this formula, not at the narrowest point. If the tape slips by half an inch the estimate can move a full percentage point, so consistency matters more than absolute precision.
The formula
US Navy circumference formulas (measurements in inches):
men: %BF = 86.010·log10(waist − neck) − 70.041·log10(height) + 36.76
women: %BF = 163.205·log10(waist + hip − neck) − 97.684·log10(height) − 78.387The result is expressed as a percentage; lean mass percentage is 100 minus body-fat percentage. For metric measurements, convert to inches first (cm ÷ 2.54).
Worked example
For the default measurements the Navy formula estimates 21.3% body fat, which falls in the Average range, and 78.7% lean mass. Change any measurement by an inch and watch how the estimate moves — that is why consistent measuring matters.
Common mistakes
- Measuring at the wrong point. A relaxed waist at the navel is not the narrowest waist. Check the standard site for the method you are using.
- Pulling the tape tight. Compressing the skin underestimates circumference and underestimates body fat. Snug, level and not compressing.
- Comparing men and women on one scale. Essential fat is roughly 2–5% for men and 10–13% for women, so the categories are sex-specific.
Frequently asked questions
How accurate is the Navy body fat formula?
Typically within 3–4 percentage points of a DEXA scan when measurements are taken carefully. It is best used to track direction of change rather than as an exact number.
Where exactly should I measure my waist?
For the US Navy method, men measure the waist horizontally at the navel. Women measure the waist at the narrowest point and the hips at the widest point.
What is a healthy body fat percentage?
Roughly 10–20% for men and 18–28% for women is often described as healthy/fitness range, but age, genetics and athletic goals all shift the target. Very low body fat can harm hormones and health.
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