How to take your measurements
The result is only as good as the measurements, so take a minute to get them right. Use a flexible, non-stretch tape, keep it level and snug against the skin without pressing in, and stand relaxed — don't pull your stomach in.
- Height — barefoot, standing straight against a wall.
- Neck — just below the larynx (Adam's apple), with the tape sloping slightly down toward the front.
- Waist (men) — horizontally around the abdomen at the level of the navel.
- Waist (women) — around the natural waist, the narrowest point between the ribs and hips.
- Hip (women) — around the widest part of the buttocks.
Measure each site two or three times and use the average. For tracking progress, measure at the same time of day, ideally in the morning.
The U.S. Navy body fat formula
This calculator uses the circumference equations developed by James Hodgdon and Marcie Beckett at the Naval Health Research Center in 1984 and long used by the U.S. military for body composition screening. With all measurements in inches:
- Men: % body fat = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76
- Women: % body fat = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387
If you enter centimeters, the calculator converts them to inches first (1 inch = 2.54 cm), so both unit systems give the same answer.
Worked examples
Man: 5 ft 10 in (70 in) tall, neck 15.5 in, waist 34 in. Waist minus neck is 18.5. The calculation is 86.010 × log10(18.5) − 70.041 × log10(70) + 36.76 ≈ 108.99 − 129.23 + 36.76 ≈ 16.5% body fat, in the "fitness" range. At 180 lb that is about 29.7 lb of fat mass and 150.3 lb of lean mass.
Woman: 5 ft 5 in (65 in) tall, neck 13 in, waist 30 in, hip 38 in. Waist plus hip minus neck is 55, giving 163.205 × log10(55) − 97.684 × log10(65) − 78.387 ≈ 28.6% body fat, in the "average" range.
Body fat categories
The American Council on Exercise (ACE) publishes these general ranges:
| Category | Women | Men |
|---|---|---|
| Essential fat | 10–13% | 2–5% |
| Athletes | 14–20% | 6–13% |
| Fitness | 21–24% | 14–17% |
| Average | 25–31% | 18–24% |
| Obese | 32% and higher | 25% and higher |
Essential fat is the minimum the body needs for normal hormone, nerve and organ function. Women naturally carry more essential fat than men. Falling below the essential range is not a goal and can be harmful.
How accurate is the tape measure method?
The Navy method is an estimate built from population data. For an individual, expect it to differ from laboratory methods such as DEXA scans or underwater weighing by several percentage points, especially for people with unusually thick necks, very muscular builds or fat stored mainly in the hips and thighs. Small measuring errors also matter: a half-inch difference at the waist can move the result by a point or more. The number is most useful for tracking change over time with consistent technique. Military branches have revised their official tape-test procedures over the years, so a current service standard may use a different method.
Body fat versus BMI
BMI uses only height and weight, so it cannot tell muscle from fat. A body fat estimate looks at where you carry size, which makes it a helpful second opinion — particularly for muscular people whose BMI looks high.
When to see a professional
If your result is in the obese range, or below the essential fat range, talk to your doctor. A clinician can measure body composition more precisely and consider other health markers before suggesting changes.
Important: results are estimates for general information only and are not medical advice. They cannot replace an assessment by a doctor, registered dietitian or other qualified health professional.
Frequently asked questions
How accurate is the U.S. Navy body fat method?
It is a reasonable estimate for most adults but can be off by several percentage points for an individual compared with a DEXA scan. Careful, consistent measuring makes the biggest difference.
Why do women need a hip measurement?
Women tend to store more fat around the hips and thighs, so the women’s equation includes the hip circumference to capture it. The men’s equation uses only the neck and waist.
What is a healthy body fat percentage?
Using the ACE ranges, roughly 14–24% for men and 21–31% for women covers the fitness and average categories. What is right for you depends on age, sport and health, so ask your doctor about a personal target.
Can I use centimeters?
Yes. Switch the units to metric and enter everything in centimeters. The calculator converts to inches internally because the published equations use inches.
Why does the calculator say my waist must be larger than my neck?
The equations take the logarithm of waist minus neck (or waist plus hip minus neck), which only works when that number is positive. If you see the message, re-check that each measurement is in the right box and unit.
Last updated: October 8, 2026