Free body fat calculator
Body fat, from a tape measure.
The US Navy circumference method — the one with published accuracy of about three to four points against a DEXA scan, and the only one you can run at home with nothing but a tape. You also get your fat mass, your lean mass, and a BMI-based estimate alongside it as a cross-check.
General wellness guidance, not medical advice. If you are pregnant, breastfeeding, under 18, or managing a medical condition, talk to a doctor or a registered dietitian before acting on any of these numbers.
How to measure so the number means something
Consistency beats precision here. The same small error repeated every month cancels out of the trend; a different error each time destroys it. So: same time of day, first thing in the morning, before eating or drinking, tape level, snug but not compressing the skin, breathing out normally rather than holding it in.
The formula is logarithmic, which is why it needs measurements rather than just weight. For men it uses waist minus neck; for women, waist plus hip minus neck. Height is in both. If the numbers you enter are physically impossible the calculator refuses rather than printing a confident nonsense figure.
What the bands mean
| Band | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletic | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Above average | 25%+ | 32%+ |
Women's numbers being higher across every band is physiology, not a different standard applied less strictly. Essential fat — the amount required for hormonal function — is roughly three times higher in women, and chasing male numbers is how menstrual and bone-density problems start.
Why this beats the scale for judging progress
Weight conflates fat, muscle, glycogen, food in transit and water. Body fat percentage does not — which is why a month of good training in a small deficit can show almost no scale movement and a visibly different tape reading. If you want to keep the lean mass while the fat goes, the protein calculator sets the target that decides it, and the deficit calculator keeps the deficit small enough to be survivable.
NutriLog AI tracks the weight side of that continuously and smooths it into a trend, so a flat fortnight reads as a flat fortnight rather than a failure.
Common questions
How accurate is the US Navy body fat method?
About three to four percentage points either way against a DEXA scan, which is respectable for something that needs only a tape measure. It is far less accurate than DEXA or a proper hydrostatic weigh-in, and far more accurate than guessing from a photo. Measured the same way each month it is genuinely useful; measured perfectly once it tells you very little.
Where exactly do I measure?
Neck: just below the larynx, tape sloping slightly down at the front. Waist: at the navel for men, at the narrowest point for women. Hips (women only): at the widest point, feet together. Keep the tape level and snug without compressing the skin, breathe out normally, and measure first thing in the morning before eating or drinking.
What is a healthy body fat percentage?
For men, roughly 10 to 20 per cent is a common healthy band, with 6 to 13 described as athletic and anything under about 5 approaching essential fat. For women the whole scale sits higher for physiological reasons — roughly 18 to 28 per cent healthy, 14 to 20 athletic, with essential fat around 10 to 13. Women needing more body fat than men is biology, not a failure of discipline.
Why does this differ from my smart scale?
Bioimpedance scales pass a small current through you and infer fat from resistance, which makes them extremely sensitive to hydration — the same body reads several points apart before and after a glass of water or a night of poor sleep. The tape method is not affected by that. Neither is a gold standard; both are most useful as a trend measured consistently.
Why does the page also show a BMI-based estimate?
As a cross-check, not a second answer. When the tape method and the BMI-derived estimate disagree by a lot, it usually means you carry more muscle than a height-and-weight equation assumes — which is exactly the situation where BMI misleads people. A close agreement is the ordinary case and tells you nothing much.
Can I lower body fat without losing weight?
Yes, and for many people it is the better goal. Eating enough protein and training with resistance while holding roughly maintenance calories moves the composition without moving the scale much — the scale stays flat and the tape keeps shrinking. It is slower than a deficit and it is why judging progress by weight alone is often discouraging for the wrong reasons.
Other free calculators
Composition changes slowly. Track it, do not guess it.
NutriLog AI logs weight, smooths the daily noise into a trend line and holds the protein target that decides how much of your loss is fat. Free, no ads, Android. Free on Google Play.