How to use it
- Choose a method. Navy / DoD uses height, neck and abdomen (men) or neck, waist and hips (women). Army one-site uses only weight and the abdomen at the navel.
- Measure with a flexible tape held level and snug against the skin without pressing in. Neck: just below the larynx (Adam’s apple). Men’s abdomen: around the navel. Women’s waist: at the narrowest point. Hips: over the widest part of the buttocks. Take each reading three times and use the average.
- Enter the numbers in inches or centimeters; the calculator gives body fat as a percentage and, if you enter your weight, the weight of fat and of everything else (lean mass).
The equations
The Navy/DoD method was developed at the Naval Health Research Center by Hodgdon and Beckett in 1984 and recommended for the whole Department of Defense in 1998. It works in inches and uses logarithms of the measurements:
| Equation (inches) | Example | |
|---|---|---|
| Men | 86.010 × log10(abdomen − neck) − 70.041 × log10(height) + 36.76 | 5 ft 10 in, neck 16 in, abdomen 34 in: 15.5% |
| Women | 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387 | 5 ft 4 in, neck 13 in, waist 28 in, hips 38 in: 26.6% |
In centimeters, each measurement is divided by 2.54 first, which is what the calculator does. In June 2023 the Army replaced this multi-site test with a one-site test (Army Directive 2023-11), built from its Comprehensive Body Composition study of more than 1,900 soldiers measured with DXA scans. It needs only weight in pounds and the abdomen at the navel in inches:
| Equation | Army’s own worked example | |
|---|---|---|
| Men | −26.97 − 0.12 × weight + 1.99 × abdomen | 210 lb, 35 in: 17.48% |
| Women | −9.15 − 0.015 × weight + 1.27 × abdomen | 165 lb, 30 in: 26.475%, reported as 26% |
How accurate is a tape measurement?
Treat the result as an estimate within a few percentage points. Studies comparing the circumference equations with laboratory methods found they tend to read too low for people with a lot of body fat and too high for very lean people, and an Army study of trainees found they missed much of the change in body fat during eight weeks of basic training. When the Army checked its old multi-site test against body scans, more than a third of men and about a quarter of women were wrongly passed or failed against the standards, which is why it moved to the one-site test. Measurement technique matters as much as the formula: a tape pulled a centimeter tighter around the abdomen changes the result by about a point.
The calculator does not label results as healthy or unhealthy. Body fat ranges vary with age and sex, there is no single accepted standard for the general public, and the military limits are fitness rules for service members. A doctor can put a result in context.
What we tested
On October 15, 2026 we checked the page’s own functions against an independent 40-digit implementation of both methods: 3,000 random sets of DoD measurements and 3,002 Army cases matched to within 1e-13 of a percentage point, the Army’s two published worked examples came out exactly (26.475% and 17.48%), and measurements that make the equation impossible (an abdomen smaller than the neck) gave a message instead of a number. In Chromium: a man 5 ft 10 in with a 16 in neck and 34 in abdomen showed 15.5% and a woman 5 ft 4 in with 13, 28 and 38 in measurements 26.6%, the same in centimeters; the Army one-site examples showed 26.5% (165 lb, 30 in) and 17.5% (210 lb, 35 in); an abdomen smaller than the neck showed a message; inputs survived a reload; the page fitted a 390 px phone with no errors. We also checked the check: changing one coefficient in the men’s equation from 70.041 to 70.41 made the comparison fail.
Sources
Checked on .
- Hodgdon JA (1999). Development of the DoD body composition estimation equations. Naval Health Research Center, DTIC ADA370158
- US Army, Fort Jackson: Army Body Fat Assessment, AD 2023-11 summary with sample calculations
- Army Public Affairs (June 12, 2023): Army publishes new body fat assessment guidance
- Taylor KM et al. (2024). Development and cross-validation of a circumference-based predictive equation to estimate body fat in an active population. Obesity Science & Practice 10(2):e747
- Frontiers in Physiology (2023): Body composition changes during 8 weeks of military training are not accurately captured by circumference-based assessments (PMC10282178)
- Army Times (June 13, 2023): No more neck or hip tape test to measure body fat, Army declares
Frequently Asked Questions
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