Body fat percentage calculator
The US Navy tape method, with a BMI-derived estimate as a cross-check.
Enter a height above zero.
Cross-check against the BMI-derived estimate
The Deurenberg equation predicts body fat from BMI and age, so it inherits everything BMI cannot see. Useful as a sanity check, not as a second opinion.
Estimating body fat from a tape measure
Body fat percentage answers the question BMI cannot: how much of your weight is fat rather than muscle, bone and water. The trouble is that measuring it properly needs equipment — hydrostatic weighing, air displacement, or a DEXA scan — and none of those fit in a browser.
What does fit is the circumference method the US Navy adopted in 1984. It estimates body fat from height and a few tape measurements, using the observation that fat accumulates in predictable places. It is not precise, and it was never meant to be: the Navy needed a consistent, cheap screening method that thousands of people could apply the same way, and that is exactly what it is.
Formulas
Worked examples
| Measurements | Body fat | Band |
|---|---|---|
| M, 180 cm, neck 38, waist 85 | 16.1% | Fitness |
| M, 175 cm, neck 40, waist 95 | 22.7% | Average |
| M, 183 cm, neck 37, waist 78 | 10.7% | Athletes |
| F, 165 cm, neck 32, waist 72, hip 96 | 26.4% | Average |
| F, 170 cm, neck 34, waist 80, hip 100 | 30.1% | Average |
All measurements in centimetres. Note how little the waist has to move to shift the result by several points.
Descriptive bands
| Band | Men | Women |
|---|---|---|
| Essential fat | 2 – 5% | 10 – 13% |
| Athletes | 6 – 13% | 14 – 20% |
| Fitness | 14 – 17% | 21 – 24% |
| Average | 18 – 24% | 25 – 31% |
| Above average | 25% and up | 32% and up |
Widely reproduced descriptive bands, not a diagnostic scale. Women carry more essential fat than men for reasons of reproductive physiology, which is why the two columns differ throughout.
Worth knowing
- The Navy method's published standard error is roughly 3 to 4 percentage points against hydrostatic weighing. A reading of 20% means "probably somewhere between 16 and 24".
- Where you put the tape changes the answer more than the equation does. Measure the waist at the navel, the neck below the larynx, and keep the tape level and snug without compressing. Measure three times and take the middle value.
- The male equation has no hip term and the female one does, which is why the two are not interchangeable and why this tool asks for different measurements.
- The Deurenberg estimate is derived from BMI, so it inherits everything BMI cannot see. It is offered as a cross-check, not a second opinion — if it disagrees wildly with the tape method, trust the tape.
Frequently asked questions
- How accurate is the US Navy body fat method?
- Its published standard error is about 3 to 4 percentage points compared with hydrostatic weighing. That is good enough to track a change in yourself over months, using the same tape and the same measuring points, and not good enough to compare against someone else or against a DEXA scan.
- Where exactly should I measure?
- Waist at the navel, breathing normally and not pulling it in. Neck just below the larynx, with the tape sloping slightly down at the front. Hips, for women, at the widest point. Keep the tape level and snug without compressing the skin, and take the middle of three measurements.
- What is a healthy body fat percentage?
- Broadly 14 to 24 per cent for men and 21 to 31 per cent for women, though these are descriptive bands from fitness organisations rather than clinical thresholds. Below roughly 5 per cent for men and 13 per cent for women is essential fat, and going under it carries real health consequences.
- Why is the estimate different from my smart scale?
- Because a scale uses bioelectrical impedance, which infers body composition from how easily a small current passes through you. That depends heavily on hydration, so the same person can read several points apart morning and evening. Neither method is a reference standard; both are more useful for tracking a trend than for a single number.