Free Body Fat Calculator
Estimate body fat percentage from neck, waist and hip measurements using the U.S. Navy method.
Enter your sex, height and your neck, waist and (for women) hip measurements. The calculator uses the U.S. Navy circumference method to estimate body fat percentage, then shows the category, fat mass and lean mass if you add your weight.
How to use the Body Fat Calculator
- Choose metric or US units and enter your own measurements.
- Read the result and the supporting numbers shown beneath it.
- Use the explanation below to see what the number means, and talk to a doctor about anything that worries you.
About the Body Fat Calculator
Estimate body fat percentage from neck, waist and hip measurements using the U.S. Navy method.
Health numbers are easier to understand when you can see how they are worked out. These calculators use published formulas and explain what the result does and does not tell you. They give general estimates and are not medical advice.
What the calculator measures
Body fat percentage is the share of your total weight that is fat. It tells you more about body composition than weight or BMI alone. The U.S. Navy method estimates it from tape measurements, so you need no equipment beyond a flexible tape.
How the U.S. Navy method works
The equations were developed for the U.S. military to screen service members. Using metric measurements in centimetres, they are:
- 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.
- Worked example for a man who is 180 cm tall with a 38 cm neck and an 85 cm waist: the estimate is about 16.1% body fat.
- Worked example for a woman who is 165 cm tall with a 32 cm neck, a 75 cm waist and 100 cm hips: the estimate is about 29.9%.
How to take the measurements
Small errors in the tape matter, so be consistent.
- Stand relaxed and measure on bare skin, breathing out normally.
- Neck: just below the larynx, tape sloping slightly down to the front.
- Waist: at the level of the navel for men and women, without pulling the stomach in.
- Hips (women): around the widest part of the buttocks.
- Take each measurement twice and use the average.
Body fat ranges
The ranges below follow the commonly used American Council on Exercise categories. They are a guide, and healthy values differ with age.
| Category | Women | Men |
|---|---|---|
| Essential fat | 10 to 13% | 2 to 5% |
| Athletes | 14 to 20% | 6 to 13% |
| Fitness | 21 to 24% | 14 to 17% |
| Average | 25 to 31% | 18 to 24% |
| Above average | 32% and above | 25% and above |
Accuracy and limits
Tape methods can be off by several percentage points and tend to be less reliable for very lean, very muscular or very heavy people. DEXA scans, underwater weighing and similar tests are more accurate but cost more and need a clinic. For most people the useful question is whether the number moves in the right direction over weeks, measured the same way each time.
Getting started with the Body Fat Calculator
Using the body fat calculator takes a minute or two. Your entries are saved in this browser, so you can come back later and carry on.
Tips for better results
Measure the same way each time: relaxed, skin-bare tape, same time of day. The method is rough, so watch the trend over several weeks rather than any single reading.
Use measurements you have taken recently, not remembered ones.
These tools give general estimates and are not medical advice. Check anything important with a doctor or registered dietitian.
Privacy and where your data goes
Everything you type into the body fat calculator stays on your own device. Zapxa does not receive your numbers or documents. If you clear your browser data, your saved entries will be removed, so download a PDF of anything you want to keep.
Frequently asked questions
How accurate is the U.S. Navy body fat method?
It is a convenient estimate and can be several percentage points off, depending on your build and how carefully you measure. Scans such as DEXA are more accurate, but cost more.
Where exactly should I measure?
Neck just below the larynx, waist at the navel (not the narrowest point), and for women the hips at the widest point. Keep the tape level and snug but not pressing into the skin.
What is a healthy body fat percentage?
It varies with age and sex. By the American Council on Exercise ranges, about 14 to 24% is fitness to average for men and about 21 to 31% for women. Essential fat is higher in women.
Why is the waist required to be bigger than the neck for men?
The formula takes the logarithm of the waist minus the neck. If the waist is not larger, the result is not defined, so re-check the measurements.
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