Estimate body fat percentage with the US Navy tape method.
This calculator uses the US Navy circumference method, developed in the 1980s as a practical field alternative to laboratory testing. It works from tape measurements and height rather than from weight, which is what lets it distinguish between two people of identical BMI with very different composition.
The women's formula includes hip circumference because fat distribution differs enough that waist alone predicts poorly.
Measurement error is by far the largest source of error in the result — a 2 cm mistake on the waist can shift the answer by 2-3 percentage points. Take each measurement three times and use the median.
| Category | Men | Women |
|---|---|---|
| Essential fat | 2-5% | 10-13% |
| Athletes | 6-13% | 14-20% |
| Fitness | 14-17% | 21-24% |
| Average | 18-24% | 25-31% |
| Obese | 25% and above | 32% and above |
Women's healthy ranges sit roughly 8-10 points above men's throughout, which is physiological rather than a matter of fitness — it reflects essential fat associated with hormonal and reproductive function. Dropping to the very bottom of the range is not a health goal for either sex; below essential levels, hormonal disruption, loss of menstrual function, impaired immunity and bone density loss follow.
BMI cannot tell muscle from fat. A 100 kg rugby player and a 100 kg sedentary man of the same height share a BMI and have nothing else in common. Because the Navy method reads waist circumference, it captures central adiposity — the fat that actually correlates with metabolic risk — and separates those two cases reasonably well.
It is still an estimate. Accuracy against hydrostatic weighing is roughly plus or minus 3-4 percentage points, and it degrades at the extremes: it tends to overestimate for very lean, muscular people, whose thicker necks skew the calculation, and it can misread people who carry fat unusually, since it assumes a typical distribution pattern.
| Method | Typical error | Practicality |
|---|---|---|
| DEXA scan | 1-2% | Clinical, costly |
| Hydrostatic weighing | 2-3% | Lab only |
| Skinfold calipers | 3-5% | Cheap, needs a trained operator |
| Navy circumference | 3-4% | Tape measure only |
| Bioelectrical impedance scales | 4-8% | Convenient, varies with hydration |
The absolute number is less useful than its direction. Because the method's error is fairly consistent for one person measured the same way, the trend is more reliable than any single reading. Measure under identical conditions — same time of day, same hydration state, same person holding the tape — every two to four weeks rather than daily. Fat loss is slow enough that weekly readings are mostly noise.
Lean mass, which the tool reports alongside, is often the more informative figure while training. Losing weight while lean mass holds steady means the loss is coming from fat, which is the outcome you want.
This is an estimate, not a medical assessment. It is not validated for children, during pregnancy, or for people with substantial oedema or unusual body proportions, and it should not be used to guide treatment.
Within about 3-4 percentage points against laboratory reference methods for most people. It is less accurate at the extremes, tending to overestimate fat in very lean muscular individuals because of neck circumference. Consistency between measurements is better than its absolute accuracy, which makes it useful for tracking change.
Women carry more essential fat, associated with hormonal and reproductive function, so healthy ranges sit 8-10 points higher. Fat distribution also differs enough that the women's formula needs hip circumference to predict reliably.
The fitness band — roughly 14-17% for men and 21-24% for women — is a reasonable target for general health. Going substantially below the athlete range is not a health improvement and carries real risks including hormonal disruption and bone density loss.
Bioelectrical impedance scales pass a small current through the body and infer composition from resistance, which is strongly affected by hydration, recent food and exercise. They can vary by several points within a single day. Neither reading is authoritative; pick one method and track its trend.
Every two to four weeks, under identical conditions. Body fat changes slowly enough that more frequent measurement mostly captures measurement error rather than real change.