Body Fat Calculator
Estimate your body fat percentage from a few tape measurements using the U.S. Navy method. It tells you how much of your weight is fat versus lean mass — a clearer picture of body composition than weight or BMI alone. No sign-up — your numbers never leave your browser.
What is the Body Fat Calculator?
The Body Fat Calculator estimates your body fat percentage from a few simple tape-measure readings, using the U.S. Navy circumference method. Instead of telling you only how heavy you are, it tells you how much of that weight is fat versus lean mass — a far more useful picture of your body composition than weight or BMI alone. Enter your sex, height, and a couple of body measurements, and the tool instantly returns your estimated body fat percentage and a fitness category, all calculated privately in your browser.
How to use it
- Choose your sex — the formula differs for men and women.
- Pick your unit system, metric (cm) or imperial (inches). Switching converts your entries instantly.
- Measure and enter your neck circumference, just below the larynx.
- Enter your waist — men measure at the navel, women at the narrowest point.
- Women also enter their hip circumference at the widest point.
- Enter your height (and optionally weight and age for fat mass and a BMI comparison).
- Your results appear instantly. Read your number and go — no button, no sign-up.
How to take the measurements
Use a flexible cloth or vinyl tape measure, keep it level and snug but not compressing the skin, and measure on bare skin or thin clothing. Stand relaxed and breathe normally — do not suck in your stomach. Measure each site two or three times and use the average for the most consistent reading. Taking measurements at the same time of day (ideally in the morning) reduces day-to-day variation.
The formula behind it
This tool uses the U.S. Navy body fat equations, which estimate body fat percentage from log-transformed circumferences and height. In inches:
Men: BF% = 86.010 x log10(waist - neck) - 70.041 x log10(height) + 36.76
Women: BF% = 163.205 x log10(waist + hip - neck) - 97.684 x log10(height) - 78.387
For comparison, the tool can also show the BMI-based estimate (the Deurenberg
equation): BF% = 1.20 x BMI + 0.23 x age - 10.8 x sex - 5.4, where
sex is 1 for men and 0 for women. The Navy method is generally more accurate
because it accounts for where fat is distributed, not just total weight.
Body fat categories
Typical reference ranges (American Council on Exercise) differ by sex:
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Acceptable | 18–24% | 25–31% |
| Above range (obese) | 25%+ | 32%+ |
Examples
- A man, 70 in tall, 38 in waist, 16 in neck: estimated body fat ≈ 21% — the acceptable range.
- A woman, 65 in tall, 30 in waist, 40 in hip, 13 in neck: estimated body fat ≈ 27% — the acceptable range.
- A male athlete, 71 in tall, 32 in waist, 16 in neck: estimated body fat ≈ 11% — the athlete range.
Common use cases
People use a body fat calculator to set a fat-loss or recomposition goal, to track changes during a cut or bulk without expensive scans, to sanity-check what a bathroom scale or BMI is really telling them, and to compare progress over weeks using a consistent, repeatable method. It is popular with lifters, runners, and anyone who wants a better signal than weight alone.
Why use this one
This calculator runs entirely in your browser, so your measurements are never uploaded, stored, or shared. It supports both metric and imperial units with instant in-page conversion, shows the Navy estimate alongside a BMI-based comparison, breaks your weight into fat mass and lean mass, and labels your result with a clear fitness category — all with no account and no app.
Results are estimates for general informational and educational purposes only and are not a medical diagnosis or a substitute for professional advice. Body fat equations can over- or under-estimate for some individuals. For health decisions, consult a qualified healthcare professional.
Frequently asked questions
How accurate is the U.S. Navy body fat method?
For most people it lands within about 3-4 percentage points of a DEXA or hydrostatic measurement, which is good for tracking trends. Accuracy depends on consistent, careful measuring and can drift for very lean, very muscular, or very tall individuals.
Is body fat percentage better than BMI?
For body composition, yes. BMI cannot tell muscle from fat, so a muscular person can look overweight by BMI while having low body fat. Body fat percentage measures the thing you usually care about directly.
Where exactly do I measure my waist?
Men measure at the navel; women measure at the narrowest part of the torso. Keep the tape horizontal all the way around and do not pull it tight enough to dent the skin.
Do I need a special tape measure?
No, any flexible cloth or vinyl tape works. Avoid a rigid metal tape, which cannot follow body curves accurately.
Can I use this for children?
No. These equations are validated for adults. Body fat assessment in children should be done by a healthcare professional with age-appropriate methods.