Body Fat Calculator

How It Works

Body fat percentage tells you how much of your weight is fat rather than muscle, bone and water — a more useful picture than weight alone. The U.S. Navy method estimates it from tape measurements: neck and waist plus height for men, neck, waist and hip plus height for women. No scales, calipers or lab visit needed.

The formulas use base-10 logarithms, with all measurements in centimeters. Men: 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450. Women: 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450. Results are grouped using the American Council on Exercise ranges.

Worked Example

A man 178 cm tall with a 38 cm neck and an 86 cm waist (waist minus neck 48 cm) measures 17.2% body fat — fitness category for men (14–17%). At 80 kg that is about 13.8 kg of fat and 66.2 kg of lean mass. A woman 165 cm tall with a 32 cm neck, 74 cm waist and 98 cm hips measures 28.4% — average for women (25–31%).

How to Use This Calculator

Choose your sex and units, then measure with a flexible tape: neck below the Adam’s apple (men) or at its narrowest (women), waist at the navel, hips at the widest point. Enter your height and, optionally, your weight for fat mass and lean mass too.

Tips and Practical Advice

Measure the same way every time — tape snug but not tight, standing relaxed — because a centimetre moves the result by a point or more. Use the trend over weeks, not one reading. The method is least accurate for very lean or very muscular people, for whom waist size reflects muscle as much as fat.

Sources: U.S. Navy body fat formula (Hodgdon & Beckett, Naval Health Research Center, 1984); categories: American Council on Exercise. Reviewed Nov 13, 2026.

Frequently Asked Questions