A body fat calculator estimates the share of your weight that is fat. The U.S. Navy method uses height and neck and waist circumference (plus hip for women) in a logarithmic equation, and gives an estimate that can be off by several percentage points. Common general-fitness ranges put average body fat at 18–24% for men and 25–31% for women.
Key takeaways
- The Navy method needs only a tape measure and your height, and women also measure hips.
- Waist is the measurement that matters most, so measure it the same way each time.
- Body fat categories here are commonly used general-fitness ranges, not diagnostic cut-offs.
- Any estimate can be off by several percentage points, so track your trend and use it alongside photos and performance.
How does this body fat calculator work?
Enter your sex, height, neck and waist circumference, plus hips if you are a woman. Weight is optional. The calculator shows your body fat percentage, the category it falls in with a five-band gauge, and, if you entered weight, your fat mass, lean mass and BMI for comparison.
It uses the U.S. Navy circumference method, which was developed from military body measurements (Hodgdon & Beckett, 1984).
How do I measure for the Navy body fat formula?
- Height: barefoot, standing straight.
- Neck: just below the larynx (Adam’s apple), tape sloping slightly down toward the front.
- Waist: for men, at the navel; for women, at the narrowest point of the waist.
- Hips (women only): around the widest part of the hips and buttocks.
Stand relaxed, breathe out normally, keep the tape snug but not tight, and measure to the nearest quarter inch (0.5 cm). Take each measurement twice and use the average. Measure at the same time of day, ideally in the morning.
The Navy body fat formula
The equations use inches and base-10 logarithms (Hodgdon & Beckett, 1984).
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
Worked examples
A 35-year-old woman who is 5′5″ and weighs 165 lb (74.8 kg) measures neck 13″, waist 32″ and hips 40″. The equation gives a body fat of 33.5%. That is 55 lb of fat and 110 lb of lean mass.
A 30-year-old man who is 5′10″ and weighs 190 lb (86.2 kg) measures neck 15.5″ and waist 34″. His body fat is 16.5%, or 31 lb of fat and 159 lb of lean mass.
Body fat percentage categories
These are the American Council on Exercise ranges, which are commonly used for general fitness guidance. They are not medical or diagnostic categories.
| Category | Women | Men |
|---|---|---|
| Essential fat | 10–13% | 2–5% |
| Athletes | 14–20% | 6–13% |
| Fitness | 21–24% | 14–17% |
| Average | 25–31% | 18–24% |
| Above average | 32% and up | 25% and up |
Essential fat is the minimum needed for basic function. Staying near it is not a goal for most people. Healthy ranges differ with age, and your doctor can tell you what is right for you.
BMI vs body fat percentage
BMI is weight divided by height squared. It can’t distinguish muscle from fat, so the two measures can disagree. The example man above has a BMI of 27.3, which is in the overweight range (CDC), yet a body fat of 16.5% that falls in the fitness range. The example woman has a BMI of 27.5 and body fat of 33.5%.
Both BMI and body fat are screening tools and neither diagnoses a condition (WHO). See the BMI calculator for the full picture of its limits.
How accurate is the Navy method?
It is a reasonable, free estimate but not a lab test. Errors of a few percentage points are normal. It assumes your fat distribution is average for your sex, so very muscular necks, unusual waist-to-hip ratios or high-fat or very lean bodies can push the result off. A tape-measure error of half an inch can move the result by about half a percentage point to a full point (an extra half inch on the waist moves the example woman up 0.6 points and the example man up 1.0).
For the best use, measure the same way every 2–4 weeks and watch the direction. Pair the result with the lean body mass calculator, and use your body fat in the BMR calculator to unlock lean-mass equations.
What should I do with my body fat number?
If you want to lose fat, set a calorie target with the calorie deficit calculator. If you want to lose fat and build muscle together, try the body recomposition calculator. If your result is at the lower end of the scale, check with a doctor before cutting calories further.
Frequently asked questions
How do I calculate body fat percentage?
Measure your height, neck and waist (and hips if you are a woman) and enter them into the U.S. Navy equation, which this calculator does for you. Alternatives include skinfold calipers, bioelectrical impedance scales and DEXA scans, each with its own error.
How accurate is the Navy body fat calculator?
It is an estimate. The method was developed from military populations and works best for people of typical build, with an error of a few percentage points compared with lab methods. It can misjudge people with very muscular necks, unusual fat distribution or very high or low body fat.
Where do I measure my waist for the Navy method?
For men, measure at the navel with the belly relaxed. For women, measure at the narrowest part of the waist. Keep the tape level and snug without compressing the skin, and measure after exhaling normally. Take each measurement twice and average.
What is a healthy body fat percentage?
Ranges depend on sex and age. The commonly used general-fitness ranges put 14–17% (men) and 21–24% (women) as fitness and 18–24% and 25–31% as average. These are not diagnostic. Ask a doctor what is healthy for you.
BMI vs body fat percentage: which is better?
They answer different questions. BMI compares weight with height and cannot tell muscle from fat, while body fat percentage estimates composition directly. Use BMI as a quick screening number and body fat percentage when you want to know what your weight is made of.
Why does my body fat differ between calculators?
Each method measures something different and carries its own error. Hydration, meals and the time of day change readings. Pick one method, use it consistently, and compare your results over weeks.
References
- Hodgdon JA, Beckett MB (1984). Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center reports (DTIC ADA143890, ADA146456).
- Centers for Disease Control and Prevention (2024). Adult BMI Calculator and categories. U.S. Centers for Disease Control and Prevention.
- World Health Organization (2024). Obesity and overweight — fact sheet. World Health Organization.