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Body Fat Calculator
This body fat calculator estimates your body fat percentage from waist, neck and hip measurements with the US Navy circumference method, or from BMI and age with the Deurenberg equation, and see your fat and lean mass.
Population-based approximations, not diagnoses. Circumference equations use inches internally; choose the formula sex category. BMI-based estimates can be inaccurate for muscular bodies. Skinfold measurement is not included.
- Estimated body fat
- 17.01%
- Estimated fat mass kg
- 12.76
- Estimated lean mass kg
- 62.24
How body fat is estimated
Circumference (US Navy method)
Equations by Hodgdon and Beckett for the US Navy. Measurements are converted to inches first.
- Men86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76
- Women163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387
BMI-based (Deurenberg 1991)
- All adults1.2 × BMI + 0.23 × age − 10.8 × sex − 5.4 (sex: men 1, women 0)
- Fat and lean massfat kg = weight × body fat % · lean kg = weight − fat kg
Age is used only by the BMI-based method. Hip is used only by the women's circumference equation. The calculator accepts ages 18 to 100.
Population-based approximations, not diagnoses. Circumference equations use inches internally; choose the formula sex category. BMI-based estimates can be inaccurate for muscular bodies. Skinfold measurement is not included.
Worked example
A 30-year-old man, 175 cm and 75 kg, with an 85 cm waist and a 38 cm neck:
| Method | Body fat | Fat kg | Lean kg |
|---|---|---|---|
| Circumference | 17.01% | 12.76 | 62.24 |
| BMI-based | 20.09% | 15.07 | 59.93 |
Circumference: waist − neck = 18.5 in and height = 68.9 in, giving 17.01%. A 90 cm waist instead of 85 cm raises it to 20.78%.
BMI-based: BMI = 75 ÷ 1.75² = 24.5, so 1.2 × 24.5 + 0.23 × 30 − 10.8 − 5.4 = 20.09%. The same body at age 50 gives 24.69%, because the equation adds 0.23 points a year.
Measuring correctly, and reading the result
Where to put the tape
- Neck: just below the larynx (Adam's apple), the tape sloping slightly down toward the front.
- Waist, men: horizontally at the level of the navel.
- Waist, women: at the narrowest point of the natural waist.
- Hips, women: at the widest point of the buttocks.
- Stand relaxed, keep the tape level and snug without compressing the skin, and read the waist after a normal breath out. Measure two or three times and use the average. Small waist errors matter: in the example, 5 cm moves the result by several points.
Body fat categories (ACE)
| 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 over | 32% and over |
A widely used fitness chart from the American Council on Exercise, not a clinical standard. Healthy ranges also shift with age.
These are estimates, not medical advice or a diagnosis. Both equations were developed from groups of adults, and an individual result can be several percentage points away from a lab measurement such as a DEXA scan. The BMI-based equation counts muscle as fat, so it reads high for muscular people. Neither is meant for children or during pregnancy. Use one method consistently to watch trends, and talk to a doctor about health decisions.
Sources: Hodgdon JA, Beckett MB, Prediction of percent body fat for U.S. Navy men and women from body circumferences and height, Naval Health Research Center Reports 84-11 and 84-29 (1984); Deurenberg P, Weststrate JA, Seidell JC. Body mass index as a measure of body fatness: age- and sex-specific prediction formulas. Br J Nutr 1991;65:105–14; American Council on Exercise, body fat percentage categories. Checked 15 October 2026.
Frequently asked questions
How do I calculate body fat with a tape measure?+
Use the US Navy circumference method: measure your height, neck and waist (and hips for women), choose Circumference and enter them in centimeters. A man 175 cm tall with an 85 cm waist and a 38 cm neck comes out at 17.01% body fat. A woman 165 cm tall with a 72 cm waist, 98 cm hips and a 33 cm neck comes out at 27.20%.
Where exactly should I measure my waist, neck and hips?+
Neck: just below the Adam's apple (larynx), with the tape sloping slightly down to the front. Waist: men at the navel; women at the narrowest point of the waist. Hips (women): at the widest point of the buttocks. Keep the tape level and snug without pressing into the skin, stand relaxed, and measure the waist after breathing out normally.
How does the BMI-based method work?+
It uses the Deurenberg (1991) equation: body fat % = 1.2 × BMI + 0.23 × age − 10.8 × sex − 5.4, where sex is 1 for men and 0 for women. A 30-year-old man who is 175 cm and 75 kg gets 20.09%. It needs no tape measure, but it can't tell muscle from fat, so it overestimates body fat in muscular people.
Which method is more accurate?+
Neither is precise. Both are population equations, and individual results can be several percentage points off. The tape method responds to your actual shape, so it usually suits athletic builds better. For the same man, the tape method gives 17.01% and the BMI method 20.09%. For a more precise measurement, a DEXA scan or air-displacement test is the reference.
What is a healthy body fat percentage?+
There are no universal cut-offs. A widely used chart from the American Council on Exercise lists average ranges of 18–24% for men and 25–31% for women, with 25% or more for men and 32% or more for women classed as obese. Women naturally carry more essential fat than men.
Why is my result different from my smart scale?+
Smart scales use bioelectrical impedance, which sends a small current through your body and is sensitive to hydration, recent meals and exercise. This calculator uses body measurements instead. Different methods often disagree by a few percentage points, so track one method over time rather than comparing them.
What are fat mass and lean mass?+
Fat mass is your weight multiplied by your body fat percentage; lean mass is everything else, including muscle, bone, organs and water. At 75 kg and 17.01% body fat, that's 12.76 kg of fat and 62.24 kg of lean mass.
Why don't men need a hip measurement?+
The US Navy equation for men uses only height, waist and neck. The women's equation adds the hips because women tend to store more fat there. The hip field is ignored when the formula sex category is Male, and the BMI-based method ignores all three tape measurements.
Can I enter inches and pounds?+
Not directly — the fields take centimeters and kilograms. Multiply inches by 2.54 and divide pounds by 2.2046: a 34-inch waist is 86.4 cm and 165 lb is 74.8 kg. The tape-method formulas convert back to inches internally, so the result is the same.
Does it work for teenagers or children?+
No. Both equations were developed for adults, and the calculator accepts ages 18 and up. Children's and teens' body composition changes as they grow, so their results are judged against age- and sex-specific growth charts by a pediatrician instead.
Are my measurements stored or uploaded?+
No. The calculation runs in your browser and nothing is uploaded or saved. Download summary saves a small text file to your own device.
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