Body Fat Calculator — U.S. Navy Method
Estimate body fat percentage from height, neck, waist, and hip measurements using the U.S. Navy method.
How to use the Body Fat Calculator
- Choose Metric (cm) or Imperial (in), then select male or female.
- Measure with a soft tape: neck just below the larynx, waist at the navel (men) or narrowest point (women), and hips at the widest point (women only).
- Enter your height and measurements to see your estimated body fat percentage and category.
About the Body Fat Calculator
This calculator estimates body fat percentage using the U.S. Navy circumference method, which relies on a handful of tape-measure measurements instead of specialized equipment like calipers or a DEXA scan. Men need height, neck, and waist measurements; women additionally need a hip measurement, since the formula differs slightly by sex to account for typical differences in fat distribution.
It accepts both metric (centimeters) and imperial (inches) units. Enter your measurements and it instantly returns an estimated body fat percentage along with a standard ACE (American Council on Exercise) category — essential fat, athletes, fitness, average, or obese — so you can see roughly where that number falls.
Worked example
Example: a man who is 180 cm tall with a 38 cm neck and an 85 cm waist has an estimated body fat of about 16.1%, which falls in the 'fitness' category.
The formula
The U.S. Navy method estimates body density from circumferences and height, then converts it to a body fat percentage. In metric units, men's body fat is 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450, and women's is 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450, with all measurements in centimeters. For example, a woman 165 cm tall with a 75 cm waist, 100 cm hips, and a 33 cm neck comes out at about 29.4%, in the 'average' range.
How to measure accurately
Small measuring differences move the result by several points, because the formula depends on the gap between the waist and neck measurements. Use a flexible tape, keep it level and snug without compressing the skin, and measure on bare skin:
- Neck: just below the larynx (Adam's apple), with the tape sloping slightly down toward the front.
- Waist (men): horizontally at the level of the navel, at the end of a normal breath out — don't hold your stomach in.
- Waist (women): at the narrowest point of the torso, usually a few centimeters above the navel.
- Hips (women): around the widest part of the buttocks, with feet together.
- Take each measurement two or three times and use the average; measure at the same time of day each time you track.
Using the result
Multiply your weight by the body fat percentage to see how much of it is fat mass: someone weighing 80 kg at 16% body fat carries about 12.8 kg of fat and 67.2 kg of lean mass. Tracking this every few weeks is more informative than weight alone, especially when you're strength training and gaining muscle while losing fat — the scale may barely move while the body fat estimate falls. Follow the trend rather than any single reading.
Frequently asked questions
- How accurate is the U.S. Navy method?
- It's reasonably accurate for most people — typically within a few percentage points of more precise methods like DEXA scans — but it's still an estimate based on circumference measurements, not a direct measurement of body fat. Measurement technique (tape tension, exact landmark placement) affects accuracy more than people expect.
- Why does the formula need a hip measurement for women but not men?
- Body fat tends to distribute differently between sexes — women typically carry more fat around the hips — so the Navy method's formula for women includes hip circumference to account for this, while the men's formula only needs neck and waist.
- What counts as a healthy body fat percentage?
- Using the ACE categories, roughly 14–17% for men and 21–24% for women is considered the 'fitness' range, while 18–24% (men) and 25–31% (women) is 'average.' Healthy ranges vary by age, goals, and individual factors, so treat these as general reference points rather than a strict target.
- Is this a substitute for a body composition scan at a clinic?
- No — this is a quick, free estimate for general tracking, not a diagnostic or clinical-grade measurement. If you need precise body composition data for a medical reason, a DEXA scan or hydrostatic weighing administered by a professional is more accurate.