Body Fat Percentage Calculator

A tape-measure estimate of body composition

Enter height, weight and the circumference measurements required by the U.S. Navy method. The calculator estimates body-fat percentage, then uses weight to show estimated fat mass and lean mass.

Weight is not part of the percentage equation. It is used only to translate the estimated percentage into mass.

Measurements used by the method

The male equation uses height, neck circumference and abdomen circumference at the navel. The female equation uses height, neck, natural waist and hip circumference.

The Navy’s body-composition guide specifies distinct measurement sites because moving the tape changes the result. Measure the neck just below the larynx. Keep the tape level, touching the skin without compressing it. Take the abdomen or waist after a normal exhale rather than holding the breath or pulling the stomach in.

For the female equation, the natural waist is the narrowest point and the hip measurement passes around the widest part of the hips.

How the equation works

The Hodgdon–Beckett circumference equations compare a circumference value against height with base-10 logarithms. The male circumference value is abdomen minus neck. The female value is waist plus hip minus neck.

The published constants expect inches. Metric entries are converted before the logarithms; using centimeters with the inch constants would produce a different and incorrect result.

Why technique matters so much

A difference of one or two centimeters can shift the estimate visibly. Tape angle, tension, breathing, food intake and measurement site all contribute. That makes a single result less informative than a consistent trend.

For tracking, use the same tape, sites, time of day and conditions. Take more than one measurement and repeat any pair that differs substantially.

An estimate is not a direct measurement

The method was developed from samples of military personnel and fitted against reference body-composition methods. Research revisiting military circumference equations finds they retain useful relationships but can be biased across individuals and groups.

Other methods also have error. Bioimpedance varies with hydration, skinfolds depend on technician skill, and even laboratory methods involve assumptions. Results from different methods should not be treated as interchangeable.

Using fat and lean mass

Fat mass is weight multiplied by the estimated percentage. Lean mass is everything left, including muscle, bone, organs and body water; it is not the same as muscle mass.

This calculator is not a diagnosis or health verdict. Body composition is only one part of health, and a clinician can interpret it alongside history, symptoms and other measurements.

Frequently asked questions

How does the Navy body-fat method work?

It compares height with sex-specific circumference measurements. For men it uses neck and abdomen; for women it uses neck, natural waist and hips. Logarithmic equations turn those measurements into an estimate.

Where should I measure my waist?

For the male equation, measure the abdomen at the navel after a normal exhale. For the female equation, measure the natural waist at its narrowest point. Keep the tape level and do not pull it into the skin.

Where should I measure my neck and hips?

Measure the neck just below the larynx with the tape level and relaxed. For the female equation, measure the hips around their widest point.

How accurate is a tape-measure estimate?

It is useful for a repeatable estimate, not an exact measurement. Equation bias plus small differences in tape position, tension, breathing and rounding can move the result by several percentage points.

Why does the calculator ask for weight if the formula does not use it?

Weight is not used to estimate the percentage. It is used only afterward to express that estimate as fat mass and lean mass.

Can I compare results from different body-fat methods?

Only cautiously. Tape equations, skinfold calipers, bioimpedance scales, air displacement and DXA measure or infer different things and each has its own error. Track one method under consistent conditions.

Is body-fat percentage a diagnosis?

No. It is one body-composition estimate and does not diagnose health, fitness or disease. A clinician can interpret measurements in the context of medical history and other findings.