Uses the U.S. Navy circumference method. Measure at the narrowest point of the waist, and around the neck just below the larynx. Estimate only, not a substitute for medical body composition testing.
What is body fat percentage, and who needs this calculator?
Body fat percentage is the share of your weight that is fat. Unlike BMI, it separates fat from muscle, bone and water. This calculator estimates it from tape measurements of your height, neck and waist, plus hip for women, using the U.S. Navy circumference method.
It helps gym-goers track fat loss beyond the weighing scale, people whose BMI looks high because of muscle, and anyone wanting a quick check before seeing a trainer or dietitian. You only need a measuring tape.
Formula used
The Navy method uses base-10 logarithms and measurements in centimetres:
- Men: Body fat % = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
- Women: Body fat % = 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.221 × log10(height)) − 450
The result is matched to commonly used fitness ranges. Men: below 6% essential fat, 6 to 14% athletic, 14 to 18% fit, 18 to 25% average, above 25% above average. Women: below 14% essential fat, 14 to 21% athletic, 21 to 25% fit, 25 to 32% average, above 32% above average.
Worked example
Take a man who is 170 cm tall with a 38 cm neck and an 85 cm waist.
- Waist − neck = 85 − 38 = 47
- log10(47) = 1.6721 and log10(170) = 2.2304
- Denominator = 1.0324 − (0.19077 × 1.6721) + (0.15456 × 2.2304) = 1.0582
- Body fat = 495 ÷ 1.0582 − 450 = 17.8%
17.8% falls in the Fit range for men.
Now a woman who is 160 cm tall with a 32 cm neck, 78 cm waist and 98 cm hip. Waist + hip − neck = 144, log10(144) = 2.1584 and log10(160) = 2.2041. Denominator = 1.29579 − (0.35004 × 2.1584) + (0.221 × 2.2041) = 1.0274. Body fat = 495 ÷ 1.0274 − 450 = 31.8%, which is in the Average range, just below the 32% line.
Frequently asked questions
How should I take the measurements?
Use a flexible tape and keep it snug but not tight. Measure the neck just below the larynx, the waist at its narrowest point and the hips at their widest. Take each measurement twice, ideally in the morning before eating.
Why does the female option ask for a hip measurement?
The Navy formula for women includes hip size because women generally store more fat around the hips and thighs. Men's results use only height, neck and waist.
What is a healthy body fat percentage?
It depends on sex and age. For most adults, the Fit and Average ranges listed above are reasonable, while very low values can be unhealthy. Athletes often sit lower, and women need more essential fat than men.
Is this as accurate as a DEXA scan?
No. It is an estimate and can be off by several percentage points. A DEXA scan or a test by a trained professional is generally more reliable.
How often should I check my body fat?
Every two to four weeks is enough. Body fat changes slowly, so daily checks mostly show measurement error rather than real change.
Limitations and accuracy
This is an estimate from a formula built on U.S. military data, so it may be less accurate for other body types, including many Indians, who often carry more body fat at the same weight. A 1 cm error in the waist moves the result by nearly one percentage point. It ignores age, muscle mass and pregnancy, and it is not a medical diagnosis.