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Body fat calculator
The tape method: a measuring tape, four numbers, and the US Navy circumference formula that gets used because it works without a laboratory. It gives your body fat percentage, plus the fat and lean mass behind it. Nothing leaves your browser.
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Taking the measurements properly
The formula is only as good as the tape work, and the tape work is where nearly all of the error lives. A centimetre at the waist moves the answer by roughly a percentage point, so it is worth doing the same way every time rather than doing it perfectly once.
- Neck. Just below the larynx, tape sloping slightly downwards at the front. Do not flex.
- Waist. At the navel for men, at the narrowest point for women. Breathe out normally and do not pull in.
- Hips. Women only, at the widest point, feet together.
- All of them. Snug against the skin without denting it, tape level the whole way round, same time of day each time. Morning, before eating, is the most repeatable.
Measure three times and take the middle. Two readings that disagree by more than half a centimetre mean the tape moved, not that you did.
Navy method and the Army tape test
This calculator runs the US Navy circumference formula: neck and waist for men, plus hips for women, against height. It is the version most people mean by "tape method" and the one most studies have checked against scans.
The US Army used a similar multi site tape for years and changed it in 2023. The Army body fat calculator now takes one tape around the abdomen at the navel, plus body weight:
| Army one site formula, inches and pounds | |
|---|---|
| Men | −26.97 − (0.12 × weight) + (1.99 × abdomen) |
| Women | −9.15 − (0.015 × weight) + (1.27 × abdomen) |
A worked example: a man weighing 180 lb with a 36 inch abdomen gets −26.97 − 21.6 + 71.64, which is about 23%. Run the same man through the Navy formula above and the answer usually lands within a few points, because both are estimating the same thing from the same waist.
The Army maximums by age
| Age | Men | Women |
|---|---|---|
| 17 to 20 | 20% | 30% |
| 21 to 27 | 22% | 32% |
| 28 to 39 | 24% | 34% |
| 40 and over | 26% | 36% |
Which one to use
If you are preparing for a service tape test, use that service's own formula, because that is the number that counts. For tracking your own progress, the Navy method here has one advantage: the neck measurement partly separates a bigger waist from a bigger frame, so it is a little less likely to punish someone who is simply broad. Whichever you pick, measure the waist the same way every time. The waist measuring guide covers the mistakes that move the number more than a month of dieting does.
What the percentage is worth knowing for
The number itself matters much less than which way it is going. Scale weight cannot tell the difference between losing three kilos of fat and losing three kilos of fat and muscle, and those are very different outcomes from the same diet. Body fat can, roughly, and roughly is enough.
The lever that decides which one happens is protein, not the size of the deficit. Enough protein and enough resistance work, and most of what you lose is fat. Neither, and a real share of it is muscle you spent years building.
| Category | Men | Women |
|---|---|---|
| Essential fat | 2 to 5% | 10 to 13% |
| Athlete | 6 to 13% | 14 to 20% |
| Fitness | 14 to 17% | 21 to 24% |
| Average | 18 to 24% | 25 to 31% |
| Above average | 25% and up | 32% and up |
Set the protein first. The protein calculator gives you a daily target in grams, and the macro calculator fits it inside your calories.
Sources
- History of the US Navy body composition program, Military Medicine, 2015
- Development and cross validation of a circumference based predictive equation to estimate body fat in an active population, Obesity Science and Practice, 2024
- Science behind policy: implementing a modern circumference based body fat equation with a physical fitness threshold, International Journal of Obesity, 2025
- International Society of Sports Nutrition position stand: diets and body composition, Journal of the International Society of Sports Nutrition, 2017
How this was made
Written by Abdullah Javaid, founder of Calfit, drafted with AI assistance and edited by hand. The result uses the US Navy circumference equations, neck and waist for men and neck, waist and hips for women, against height. The Army section reproduces the one site equation published with the 2023 change to Army Regulation 600-9, and the categories are the American Council on Exercise ranges most tape calculators report.
Quick questions
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