Body Fat Calculator.
Estimate your body fat percentage using the US Navy Method. All you need is a tape measure. More predictive of health risk than BMI alone.
Frequently Asked Questions
How does the US Navy body fat method work?+
It estimates body fat from circumference measurements rather than from weight. Men supply height, neck and waist; women add hip. Those go into a logarithmic formula developed for the US Navy, which returns a body fat percentage and, from that, your lean body mass. All you need is a tape measure.
How accurate is the Navy method?+
Typically within about three to four percentage points of a DEXA scan for most people, which is good enough to track direction over months and not good enough to argue about a single point. It is least accurate at the extremes (very lean or very heavy), and it cannot tell where the fat sits, only how much there is.
Where exactly do I measure?+
Neck just below the larynx with the tape sloping slightly downward at the front. Waist at the navel for men, at the narrowest point for women. Hips at the widest point. Keep the tape snug but not compressing the skin, measure on bare skin, and do it at the same time of day each time. Measurement inconsistency causes more apparent change than actual fat loss does.
Do I need calipers or a smart scale?+
No. That is the point of this method: it was designed to be run on thousands of people with nothing but a tape measure. Calipers require practice to be reliable, and bioimpedance scales swing with how hydrated you are.
What is a healthy body fat percentage?+
Broadly, 10–20% for men and 18–28% for women covers the healthy range, with athletes below and the risk zone above. Essential fat (the minimum needed for normal function) is around 3% for men and 12% for women, and sustained levels near it are not healthy. Age shifts the whole range upward slightly.
Why does the calculator also show lean body mass?+
Because it is usually the more useful number. Fat percentage can fall simply because you lost muscle, which is not the outcome anyone wants. Watching lean mass alongside it tells you whether a drop in body fat came from losing fat or from losing the tissue you were trying to keep.
What the US Navy method actually measures.
The US Navy formula estimates body fat percentage from circumference measurements (neck and waist for men, plus hip for women) combined with height. It was developed and validated by Hodgdon and Beckett at the Naval Health Research Center in 1984 as a field-deployable alternative to hydrostatic weighing for screening service members. It is a regression equation, not a direct measurement.
Against the laboratory gold standards (DEXA scan, hydrostatic weighing, BodPod), the US Navy method typically lands within ±3–4% for adults with average body composition. It tends to overestimate fat in very muscular individuals (large necks) and underestimate it in adults carrying weight predominantly in the limbs rather than the trunk.
Why this beats BMI for almost everyone.
BMI cannot separate muscle from fat. Two adults at the same height and weight (one lean and muscular, one sedentary) get identical BMI scores but radically different metabolic risk. The US Navy method side-steps that confound by sampling where fat actually accumulates: the waist (visceral and subcutaneous abdominal fat) and, for women, the hips (gynoid fat).
Body fat percentage also gives you a lever BMI cannot: lean body mass. Knowing your fat-free mass lets you set protein targets, refine TDEE estimates, and judge whether a weight change came from fat or muscle. It is the single most useful number to track over a cut or bulk.
How to interpret your number.
Reference ranges from the American Council on Exercise: essential fat is 10–13% (women) / 2–5% (men); athletes 14–20% / 6–13%; fitness 21–24% / 14–17%; average 25–31% / 18–24%; obese 32%+ / 25%+. Risk for cardiometabolic disease climbs sharply above the average band and the gain comes mostly from visceral, not subcutaneous, fat.
Track the trend, not the absolute number. The error bars on any field method are wide enough that a single reading is noisy, but month-over-month change at the same measurement protocol (same tape, same time of day, same hydration state) is a reliable signal.
When this estimate is wrong for you.
Three populations where the Navy formula breaks: bodybuilders or strength athletes with disproportionately large neck circumferences (overestimates fat by 3–6%); adults with central obesity but minimal hip/limb fat (overestimates); and adults who carry fat predominantly in extremities rather than the trunk (underestimates). If you fall in any of these groups, a DEXA scan ($75–$150) is worth the one-time spend for a baseline.
- Hodgdon JA, Beckett MB. (1984). Prediction of percent body fat for U.S. Navy men from body circumferences and height. Naval Health Research Center, Report No. 84-11.
- Hodgdon JA, Beckett MB. (1984). Prediction of percent body fat for U.S. Navy women from body circumferences and height. Naval Health Research Center, Report No. 84-29.
- Cui Z, Truesdale KP, Cai J, Stevens J. (2014). Evaluation of anthropometric equations to assess body fat in adults: NHANES 1999–2004. Med Sci Sports Exerc, 46(6), 1147–1158.
Body-fat percentage only matters as a trend. Log it next to waist and weekly delta and watch the line, not the day-to-day noise.
Get the guide →For education, not medical advice. Results are estimates, not a diagnosis. Discuss any abnormal value or health concern with a qualified clinician.
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