Body Fat Calculator
Estimate body fat from neck, waist and hip measurements, with a BMI-based sanity check beside it.
| Body fat (tape method) | 17.3% Fitness |
|---|---|
| Fat mass | 13 kg (28.6 lb) |
| Lean mass | 62 kg (136.8 lb) |
| BMI method estimate | 19.1% 1.20 x BMI + 0.23 x age - 10.8 x sex - 5.4 |
| BMI | 23.7 Normal weight |
Reference bands, not your result; the table above gives the category for the measurements you enter.
What body fat percentage tells you
Body fat percentage is the share of your body weight held as fat tissue. It is a far better description of body composition than weight alone, because the same kilogram can be muscle, fat or water and each has a very different effect on health, strength and appearance. Two people at 80 kg can differ by 15 percentage points of body fat, which is the difference between a lean athlete and someone with obesity.
Percentages are also not a scoreboard. Some fat is essential: it cushions organs, stores fat-soluble vitamins and supports hormone production. Athletic ranges are achievable only for people who train and eat for them, and for many people they are neither necessary nor healthy to hold year-round.
| Category | Men | Women |
|---|---|---|
| Essential fat | 2% to 5% | 10% to 13% |
| Athletic | 6% to 13% | 14% to 20% |
| Fitness | 14% to 17% | 21% to 24% |
| Average | 18% to 24% | 25% to 31% |
| Obesity | 25% and above | 32% and above |
How the US Navy tape method works
The Navy method uses circumference measurements in a logarithmic equation. For men it needs neck and waist; for women it needs neck, waist and hip. The logic is simple: the abdomen grows faster than the neck as body fat rises, so the ratio between them tracks fat reasonably well without expensive equipment.
All measurements are entered in centimetres or inches depending on the unit switch above, and the page converts internally. A waist measurement that is smaller than the neck returns 'check measurements' rather than a number, because the equation is undefined there and a fabricated result would be worse than none.
Reading your result
The first row is the tape estimate and the category it falls into. The second and third rows convert it into fat mass and lean mass in kilograms and pounds, which is usually more useful for tracking than the percentage: if you lose 3 kg and your lean mass is unchanged, the fat loss is real and the plan is working.
The BMI cross-check row uses a separate equation and will not match the tape estimate exactly. When the two disagree by more than about five percentage points, one of the inputs is off - commonly a waist measured over clothing, a neck measured too low, or a genuinely muscular body that the BMI-based equation cannot describe. Trust the tape if the measurements were taken carefully, and treat the gap as information about how unusual your build is.
How accurate is a tape measurement?
Published comparisons against hydrostatic weighing and DEXA put the Navy method within roughly 3 to 4 percentage points for most people, which is good for a tape measure and clearly worse than a laboratory scan. The error is not random: it tends to underestimate fat in very lean, muscular people and overestimate it in people with obesity, because the equation assumes an average distribution of fat.
Consistency matters more than absolute accuracy for tracking. Measure the same way, at the same time of day, with the same tape tension, and compare results to your own previous numbers rather than to a chart. A 1% change that is repeatable tells you more than an absolute figure with a four-point error bar.
Other ways to measure body fat
Each method trades cost and access against precision. DEXA is the practical reference standard for most people, at the price of a clinic visit. Hydrostatic weighing and bod-pod are accurate but rare. Calipers need a trained tester to be useful; done casually by a partner they are roughly as good as a tape. Bioelectrical impedance scales are convenient and highly sensitive to hydration, so their day-to-day readings can swing several percentage points.
| Method | Typical error | Best used for |
|---|---|---|
| DEXA scan | 1% to 2% | an accurate baseline every 6 to 12 months |
| Hydrostatic weighing | 2% to 3% | research and clinic settings |
| Skinfold calipers | 3% to 5% | tracking when the same tester measures each time |
| Navy tape method | 3% to 4% | frequent, free tracking with a tape measure |
| Impedance scale | 3% to 8% | trends only, measured under the same conditions |
Measuring so the number means something
Take measurements first thing in the morning, before eating, with the tape snug but not compressing the skin. For the neck, measure just below the larynx with the tape sloping slightly down at the front. For the waist, use the narrowest point for men and the widest point for women, at the end of a normal breath rather than sucked in. Measure each site twice and average.
- Keep the tape level and parallel to the floor at the waist.
- Do not pull the tape tight enough to indent the skin.
- Measure on bare skin, not over clothing.
- Repeat at the same time of day and note the date.
Frequently asked questions
What is a healthy body fat percentage?
For men roughly 14% to 24% is the common 'average to fitness' band, and for women 21% to 31%. Athletic ranges are lower, and essential fat - about 2% to 5% for men and 10% to 13% for women - is the floor below which health is at risk.
How accurate is the Navy method?
Within about 3 to 4 percentage points of a laboratory measurement for most people. It tends to underestimate fat in very muscular people and overestimate it in heavier people, so treat the trend as more reliable than the absolute number.
Do I need to measure my hip?
For women, yes - the navy equation uses neck, waist and hip. For men, only neck and waist are needed. The hip field is simply ignored if you are using the male equation.
Why does my scale disagree with the tape?
Impedance scales estimate fat from the speed of a small current through your body, which depends heavily on hydration and recent food. Hydration changes can move a scale reading by several percentage points in a single day, while the tape is largely unaffected.
Is body fat percentage better than BMI?
For describing an individual, usually yes: BMI cannot tell muscle from fat, so muscular people come out too high and people with low muscle mass come out too low. BMI remains useful for population screening because it needs only height and weight.
How often should I measure?
Every two to four weeks is enough. Weekly measurements pick up more measurement noise than real change, and daily readings are meaningless for this method.
Sources
- Hodgdon JA, Beckett MB, Prediction of percent body fat for US Navy men and women
- WHO: Body mass index
- American Council on Exercise: Body fat percentage ranges
Formulas and thresholds are taken from the sources above. They are a starting point for adults, not a diagnosis.
Last reviewed September 12, 2026. How we calculate · Editorial policy