Body Fat Calculator
Estimate body fat with the US Navy tape method, plus fat and lean mass.
Estimate Body Fat From Tape Measurements
Body fat percentage is a more useful figure than weight, because it distinguishes between the two kinds of mass that a scale adds together. Measuring it accurately requires a DEXA scan; estimating it reasonably requires a tape measure and a formula.
The US Navy circumference method is the one used here. It is not precise — expect roughly ±3 percentage points against DEXA — but it is consistent, which means the trend over weeks is informative even when the absolute number is not exact. Everything is calculated in your browser and nothing is recorded.
Key features
- US Navy circumference method — the standard tape-measure formula, with the correct separate equations for each sex.
- Metric and imperial — centimetres and kilograms, or inches and pounds.
- Lean mass in real weight — enter your weight and the tool shows the lean kilograms behind the percentage, which is what changes when training works.
- Category guidance — where the result sits against the usual essential, athletic, fitness and average bands.
- Weight is optional — the percentage needs only the tape measurements; weight is what turns it into a mass.
This tool runs entirely inside your browser using native Web APIs. Your files and text are never uploaded to a server, never logged and never shared with third parties.
How to use: Body Fat Calculator
- Choose units and sex
The formula uses different equations, so this affects the result. - Measure your neck and waist
Neck below the larynx, waist at the navel. Tape snug but not compressing. - Add hip measurement if female
At the widest point. The female equation requires it. - Read the estimate
Body fat percentage and its category appear at once; add your weight to see the lean mass behind it.
Technical specifications
| Processing location | Entirely in your browser — no server round trip |
|---|---|
| Data uploaded | None. Files and text never leave your device |
| Price | Free — no account, no trial, no usage cap |
| Category | Calculators |
| Works offline | Yes, once the page has loaded |
| Browser support | Chrome 90+, Edge 90+, Firefox 90+, Safari 15+ |
| Interface languages | English, 中文, हिन्दी, Español, العربية |
Frequently asked questions
How accurate is the Navy method?
Around ±3 percentage points against DEXA for most people, with larger errors at the extremes of body composition. Its real strength is repeatability: measured the same way each time, the direction of change is reliable even if the absolute figure is not.
Why is measurement technique so important?
Because the formula is logarithmic and sensitive to the waist figure in particular. A centimetre of difference from pulling the tape tighter can shift the result by more than a point. Measure the same way, at the same time of day, every time.
What is a healthy body fat percentage?
Broadly, 10–20% for men and 18–28% for women is considered healthy, with athletes lower and essential minimums around 3% and 12% respectively. Below those minimums is dangerous, not impressive.
Is my health data stored?
No. Everything is calculated in the page. Nothing is transmitted, saved or shared — and this is an estimate, not a medical assessment.