Body Fat Calculator
Estimate your body fat percentage using the US Navy method with waist, neck, and hip measurements.
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How to use this calculator
Men: 495/(1.0324−0.19077×log10(waist−neck)+0.15456×log10(height))−450. Women: add hip measurement.
- 1
Select your biological sex.
- 2
Enter your height in cm.
- 3
Measure your waist circumference at the navel and enter it.
- 4
Measure your neck circumference at the narrowest point and enter it.
- 5
Women: also measure your hip circumference at the widest point.
- 6
The result estimates your body fat percentage and fitness category.
Frequently asked questions
Which formula is used for men?
The US Navy circumference formula in metric form: 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450, with all measurements in centimetres. Hips are ignored for men, so leave that field alone.
And for women?
The female version adds the hip: 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450, again in centimetres. If the hip is zero (which is also what a cleared box becomes) for a female entry, the calculator asks for it instead of guessing.
How does it handle impossible inputs?
Height, waist and neck must be positive. For men the waist must exceed the neck, because the formula takes the logarithm of their difference, and for women waist plus hip must exceed the neck. Otherwise you get an error message instead of a number. Results are also clamped to between 0% and 60%.
What do the category names mean?
They are cut-offs in the code. For men: under 6% Essential fat, under 14% Athletic, under 18% Fitness, under 25% Average, otherwise Obese. For women: under 14%, under 21%, under 25%, under 32%, otherwise Obese. The labels are informal descriptors and not diagnoses.
How much does a measurement error matter?
A lot, because the formula is sensitive to the waist and neck figures. With the default man, 84 cm gives 16.9% (Fitness), 85 cm gives 17.7% (Fitness) and 86 cm gives 18.5%, which tips into Average. Measure at the same landmark each time and repeat the tape reading.
Can I enter inches?
No. All fields are in centimetres. Multiply inches by 2.54 first. Entering inch values directly gives an unreliable percentage, since the formula expects centimetres.
Is this a medical measurement?
No. It estimates body fat from tape measurements and does not take weight, age or muscle into account. Scans such as DEXA measure body composition directly. This is general information, not medical advice, and a healthcare professional can interpret body composition for you.
Body fat from tape measurements — the US Navy method in the calculator
Measurements in, a percentage out
The tool needs your height, a waist measured at the navel and a neck measurement, plus a hip measurement for women. It inserts them into the logarithmic Navy formula for your sex and reports a single body fat percentage with a category label. Body weight is not used at all, which means the estimate is driven entirely by how large your waist is relative to your neck and height. The output is clamped to a range from 0% to 60%.
Category cut-offs used by the code
The label is a simple lookup against these upper limits.
| Category | Men | Women |
|---|---|---|
| Essential fat | under 6 | under 14 |
| Athletic | 6 to under 14 | 14 to under 21 |
| Fitness | 14 to under 18 | 21 to under 25 |
| Average | 18 to under 25 | 25 to under 32 |
| Obese | 25 or more | 32 or more |
Worked examples
Every figure was produced by running the calculator. A man 175 cm tall with an 85 cm waist and 37 cm neck gets 17.7%, labelled Fitness. A man 180 cm tall with a 100 cm waist and 40 cm neck gets 25.2%, labelled Obese. A woman 165 cm tall with a 75 cm waist, 32 cm neck and 98 cm hips gets 28.9%, labelled Average. A man at 175 cm with a 70 cm waist and a 40 cm neck gets 1.1%, which shows how a thick neck against a slim waist can give an implausibly low estimate.
How to measure for the formula
Use a flexible tape and keep it level. Take the waist at the navel, relaxed, after breathing out normally, and the neck just below the larynx with the tape sloping slightly down at the front. Women should measure the hips at the widest point. Make two readings and use the average. Because one centimetre can shift the result by nearly a percentage point, take every measurement the same way each time you re-check.
Where the method falls short
Circumference formulas assume your body is shaped like the people the equation was built from. Unusually large necks, athletes with thick shoulders, and people who carry weight in unusual places can give odd values. The percentage is also clamped, so values at the clamp are not meaningful. For a precise number, a body-composition scan is the usual choice. This page is general information, not medical advice.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →