US Navy Body Fat Percentage Calculator (Tape Measure Method)

Estimate your body fat percentage, fat mass, lean body mass, and ACE fitness category with simple circumference measurements.

Estimating body fat percentage with the US Navy formula

The US Navy method estimates body fat percentage from height and tape-measured circumferences: neck and waist for men, plus hips for women. For a man of 178 cm with a 39.5 cm neck and an 86.5 cm waist, the tool gives about 16.4%.

Formulas (measurements in cm)

  • Men: %BF = 495 / (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
  • Women: %BF = 495 / (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450

The result is capped between 2% and 65%. Fat mass is weight × %BF / 100; lean mass (muscle, bone, water) is the rest. In US units the tool first converts inches and pounds to cm and kg.

Examples

Man, 178 cm, 82 kg, neck 39.5 cm, waist 86.5 cm: 16.4% body fat, i.e. 13.5 kg fat mass and 68.5 kg lean mass, "fitness" category. Woman, 165 cm, 62 kg, neck 33 cm, waist 75 cm, hips 96.5 cm: 27.7%, i.e. 17.2 kg and 44.8 kg, "acceptable average".

Categories shown

American Council on Exercise (ACE) chart, from a fitness certification body: men 2-5% essential fat, 6-13% athletes, 14-17% fitness, 18-24% average, 25% and above excess; women 10-13%, 14-20%, 21-24%, 25-31%, 32% and above. It is a popular reference, not a medical standard.

Limits

Unlike BMI, the method reflects body shape, but it remains a statistical estimate: the gap with a reference measurement (underwater weighing, DEXA) is commonly a few points. Tape accuracy matters; measure the neck just below the larynx and a man's waist at the navel. Age is not used in the calculation.

Method and sources

Both equations were derived in 1984 by Hodgdon and Beckett at the Naval Health Research Center in San Diego, from service members whose body density had been measured by underwater weighing: 602 men in report no. 84-11 and 214 women in report no. 84-29. The tool uses the metric form, which gives body density, converted to body fat percentage with the Siri equation (495 ÷ density − 450). The inch-based form, more common in the United States, lands within a few tenths of a point: 16.5% instead of 16.4% for the man in the example, 28.0% instead of 27.7% for the woman.

"US Navy" refers to where the equation comes from, not to a current military rule. Since its 10 March 2022 version, Department of Defense instruction DoDI 1308.03 (DoD Physical Fitness/Body Composition Program, amended on 25 June 2025) no longer requires the tape test: each service chooses between a body fat calculation, waist-to-height ratio, abdominal circumference, height-weight screening or a combination. In 2026 the US Army adopted waist-to-height ratio alone, with a 0.55 threshold (Army Directive 2026-13).

The categories follow the American Council on Exercise chart; a 2018 ACE article confirms its obesity thresholds of 25% for men and 32% for women. This estimate does not replace a laboratory measurement (DEXA, underwater weighing) or advice from a doctor or dietitian. References as of 22/10/2026.

Frequently Asked Questions

How do I take measurements for the US Navy method?

Measure the neck just below the larynx and, for men, the waist at the navel; women add the hips at the widest point. Keep the tape level without compressing the skin. A 1 cm error on the waist shifts the result by roughly 0.5 to 0.8 points in the tool's examples.

How accurate is the US Navy formula?

It is a statistical estimate developed in 1984 by Hodgdon and Beckett from underwater weighing of Navy personnel. The gap with a reference measurement is commonly a few percentage points, larger for very muscular people or unusual body shapes.

What body fat percentage is considered normal?

The American Council on Exercise chart used by the tool puts the average at 18-24% for men and 25-31% for women. It flags excess fat from 25% for men and 32% for women. It is a fitness reference, not a medical standard.

What is the difference between body fat and BMI?

BMI only uses weight and height, while the US Navy method uses neck, waist and hip circumferences to estimate the share of fat. A man of 178 cm and 82 kg has a BMI of 25.9 (overweight), yet with an 86.5 cm waist the tool estimates 16.4% body fat.

Is this tool really free?

Yes, all tools on Kristools are 100% free and accessible without registration.

Is my data protected?

Yes. All processing is performed directly and securely inside your browser. No personal data is sent to our servers.