Body Fat Calculator
Estimate your body fat percentage from height, neck, waist and hip measurements with the US Navy formula, in centimetres or inches.
Estimate based on published formulas, not medical advice. Talk to a health professional about your situation.
Men: measure the waist horizontally at the navel. Women: measure the waist at its narrowest point and the hips at their widest. Neck: just below the larynx.
- Body fat
- –
- Category (ACE)
- –
- Fat mass
- –
- Lean mass
- –
| Category | Women | Men |
|---|---|---|
| Essential fat | 10–13 % | 2–5 % |
| Athletes | 14–20 % | 6–13 % |
| Fitness | 21–24 % | 14–17 % |
| Average | 25–31 % | 18–24 % |
| Obese | ≥ 32 % | ≥ 25 % |
How to use the body fat calculator
- Choose Metric (cm, kg) or Imperial (ft, in, lb).
- Select Male or Female. The Hips field appears for women, because their equation uses it.
- Enter your Height, Neck and Waist measurements (and Hips for women).
- Optionally enter your weight in Weight (optional) to see your Fat mass and Lean mass.
- Read your Body fat percentage and its Category (ACE). The matching row of the table is highlighted, and the calculation steps are listed.
The result updates as you type, entirely in your browser. Clear empties the fields.
How to measure
Use a flexible tape measure, keep it horizontal and snug without compressing the skin, and measure on bare skin after breathing out normally. Take each measurement two or three times and use the average.
- Neck: just below the larynx (Adam’s apple), with the tape sloping slightly downward to the front.
- Waist, men: horizontally at the level of the navel.
- Waist, women: at the narrowest point of the waist, usually between the navel and the bottom of the ribs.
- Hips, women: at the widest point of the buttocks.
- Height: without shoes, standing straight against a wall.
The US Navy formula
The circumference method was developed by James Hodgdon and Marcie Beckett at the Naval Health Research Center (reports 84-11 for men and 84-29 for women, 1984). It predicts body density from measurements in centimetres:
- men: density = 1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)
- women: density = 1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)
Density is then converted to a fat percentage with Siri’s equation: body fat % = 495 ÷ density − 450. Inches are converted to centimetres first, so the result matches the inch-based version of the formula used by the US Department of Defense to within a few tenths of a percent.
Example: a man 178 cm tall with a 50 cm neck and a 96 cm waist has a density of 1.0630 and about 15.7 % body fat.
When you enter a weight, fat mass = weight × body fat % and lean mass = weight − fat mass.
Body fat categories
The table uses the categories of the American Council on Exercise (ACE):
| Category | Women | Men |
|---|---|---|
| Essential fat | 10–13 % | 2–5 % |
| Athletes | 14–20 % | 6–13 % |
| Fitness | 21–24 % | 14–17 % |
| Average | 25–31 % | 18–24 % |
| Obese | 32 % and more | 25 % and more |
Essential fat is the minimum the body needs for hormones, nerves and organs. Going below it is dangerous, and it is not a goal.
Accuracy and limitations
The Navy method is practical and cheap, but it is an estimate. Compared with laboratory methods such as underwater weighing or DXA, typical errors are around 3 to 4 percentage points, and more for very lean, very muscular or very heavy people, whose body shape differs from the military population the formula was built on. Small measuring errors matter: one centimetre on the waist can change the result by close to one point. Measure at the same time of day, under the same conditions, if you track changes.
The equations are designed for adults and are not suited to children, pregnancy or some medical conditions. A body fat percentage is only one health marker among many. For a full assessment, or before starting a significant diet or training plan, talk to a doctor or registered dietitian.
Frequently asked questions
How accurate is the US Navy body fat method?
For most adults, it lands within about 3 to 4 percentage points of laboratory measurements. It is good for tracking changes over time with consistent measuring, less so for a one-off exact figure.
Why do women need a hip measurement?
Women store proportionally more fat around the hips and thighs, so the women’s equation adds hip circumference to improve the prediction.
What is a healthy body fat percentage?
The ACE “fitness” and “average” ranges (14–24 % for men, 21–31 % for women) are common reference points. Healthy ranges also depend on age, so ask a professional to interpret your result.
Why is my result different from my smart scale?
Scales use bioelectrical impedance, which is sensitive to hydration, meals and exercise. Both methods are estimates and can differ by several points.
Can I use this calculator if I am very muscular?
You can, but a thick neck or a muscular waist can shift the estimate. A method such as DXA gives a more reliable figure for athletes.
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- BMR Calculator Estimate your basal metabolic rate with the Mifflin-St Jeor and revised Harris-Benedict equations, in metric or imperial units, with every step shown.
- TDEE and Daily Calorie Calculator Estimate your total daily energy expenditure (TDEE) and maintenance calories from your BMR and activity level, in metric or imperial units.