Body Fat Calculator
The US Navy method estimates body fat from a tape measure. A man who is 180 cm tall with a 38 cm neck and an 85 cm waist comes out at about 16.1 percent body fat. It is an estimate and can be off by several points.
How to use
- Choose your sex and units, then enter your height. Add your weight if you also want fat mass and lean mass.
- Measure your neck just below the larynx, and your waist: for men at the navel, for women at the narrowest point. Women also measure the hips at the widest point. Keep the tape snug and level, not pulled tight.
- Read your estimated body fat percentage, the category and, if you gave your weight, the fat and lean mass.
How it works
The US Navy formula (Hodgdon and Beckett, 1984) works in centimeters. Men: body fat % = 495 / (1.0324 - 0.19077 x log10(waist - neck) + 0.15456 x log10(height)) - 450. Women: 495 / (1.29579 - 0.35004 x log10(waist + hip - neck) + 0.22100 x log10(height)) - 450.
For a man 180 cm tall with a 38 cm neck and an 85 cm waist, waist minus neck is 47 cm, which gives about 16.1 percent. Fat mass is weight times body fat percent, and lean mass is the rest.
Categories follow the American Council on Exercise (ACE). Men: essential fat 2 to 5 percent, athletes 6 to 13, fitness 14 to 17, average 18 to 24, obese 25 and above. Women: essential 10 to 13, athletes 14 to 20, fitness 21 to 24, average 25 to 31, obese 32 and above.
Tape methods are estimates and typically differ from DEXA scans by several percentage points. Small measuring errors matter: 1 cm on the waist changes the result by roughly 1 point. This is not medical advice. Ask a doctor about your health.
ACE body fat categories
| Category | Men | Women |
|---|---|---|
| Essential fat | 2 to 5% | 10 to 13% |
| Athletes | 6 to 13% | 14 to 20% |
| Fitness | 14 to 17% | 21 to 24% |
| Average | 18 to 24% | 25 to 31% |
| Obese | 25% and above | 32% and above |
Sources and disclaimer
Formula: Hodgdon JA and Beckett MB, "Prediction of percent body fat for U.S. Navy men and women from body circumferences and height", Naval Health Research Center reports 84-11 and 84-29, 1984. Categories: American Council on Exercise, "What are the guidelines for percentage of body fat loss?".
This tool is not medical advice. See a doctor for a health assessment.
Last reviewed 2026-10-13
FAQ
How accurate is the Navy body fat method?
It is a quick estimate. Studies find it correlates with more precise methods but can be off by roughly 3 to 4 percentage points for an individual. DEXA, hydrostatic weighing or a clinical assessment are more accurate.
Where exactly should I measure?
Neck: just below the larynx, tape sloping slightly down at the front. Waist: men at the navel, women at the narrowest point. Hips: at the widest point of the buttocks. Measure bare skin, standing relaxed, and take the average of two readings.
What is a healthy body fat percentage?
It depends on age and sex. The ACE ranges are a common reference: roughly 14 to 24 percent for men and 21 to 31 percent for women covers fitness to average. Essential fat is the minimum needed for health and should not be a target.
Is my data sent anywhere?
No. The calculation runs in your browser and nothing you enter is sent to a server.