Body fat calculator
Body fat calculator: the US Navy tape method, with healthy ranges
Measure your neck, waist (and hips, for women) and height to estimate your body fat percentage with the US Navy tape method. The result comes with its honest error, typically ±3.5 to 6 points, and the body fat range that matches a healthy BMI for your age and sex.
Estimate your body fat
For adults. Measure on the skin with a flexible tape, relaxed, at the end of a normal breath out.
Example: woman, 32, 165 cm, neck 33, waist 76, hips 100 cm
Estimated body fat
30%
Typical error
±3.5 to 6 points
At a healthy BMI, age 20–39
21–33%
How the US Navy method works
The US Navy and the other US military services used this method for decades. It estimates body fat from circumferences and height, using equations built by comparing tape measurements with underwater weighing in 602 Navy men and 214 Navy women. In the form the US Department of Defense adopted in 2002, with measurements in inches:
| Group | Equation (log10, inches) |
|---|---|
| Men | 86.010 × log(abdomen − neck) − 70.041 × log(height) + 36.76 |
| Women | 163.205 × log(waist + hip − neck) − 97.684 × log(height) − 78.387 |
Rounded to whole numbers, these equations reproduce every cell of the Navy’s official lookup tables. The calculator converts centimetres to inches first. For a man of 178 cm with a 90 cm abdomen and a 38 cm neck they give 20%, and for the woman in the example above 30%.
How to measure
| Measurement | Where | Tip |
|---|---|---|
| Neck | Just below the Adam’s apple, with the tape at a right angle to the neck | Keep your shoulders down; don’t measure over the Adam’s apple |
| Abdomen (men) | Around the navel, level with the floor | Measure at the end of a normal breath out, arms at your sides |
| Waist (women) | The narrowest point, usually about halfway between the navel and the bottom of the breastbone | If it’s unclear, take a few and use the smallest |
| Hips (women) | The widest part of the buttocks, seen from the side | Keep the tape level |
Measure your height without shoes, in the same unit as the tape. The services take each measurement two or three times and average them. A tape pulled too tight, or a waist measured at a different spot next time, changes the result more than a week of training does.
How accurate is it?
When the equations were built, their typical error against underwater weighing was about 3.5 percentage points. Against modern DXA scans the error is larger. In 1,904 US soldiers measured in 2021–22, the equations read low on average, especially in men:
So treat the number as a range, and use the trend. Measured the same way every few weeks, a falling estimate is more meaningful than any single reading. Bioimpedance smart scales and other tape equations have their own errors, so their numbers won’t match this one.
What’s a healthy body fat percentage?
There’s no single official cut-off. One widely used reference, Gallagher et al. (2000), worked out the body fat that corresponds to the healthy BMI range by age and sex. The authors call these ranges provisional.
| Group | Below healthy BMI | At a healthy BMI | At an overweight BMI | At an obese BMI |
|---|---|---|---|---|
| Women, 20–39 | under 21% | 21–33% | 33–39% | 39% or more |
| Women, 40–59 | under 23% | 23–34% | 34–40% | 40% or more |
| Women, 60–79 | under 24% | 24–36% | 36–42% | 42% or more |
| Men, 20–39 | under 8% | 8–20% | 20–25% | 25% or more |
| Men, 40–59 | under 11% | 11–22% | 22–28% | 28% or more |
| Men, 60–79 | under 13% | 13–25% | 25–30% | 30% or more |
These values come from African American and white adults; the study’s “Asian” group was Japanese. People of South Asian background tend to carry more body fat at the same BMI. India’s 2025 revised definition of obesity (Misra et al.) treats more than 25.5% body fat in men and 38% in women as obesity.
Body fat, BMI or waist?
A 2025 Lancet commission on obesity recommends using BMI for screening, not as an individual measure of health, and confirming excess fat with a direct measurement where available, or with at least one of waist circumference, waist-to-hip ratio or waist-to-height ratio. A tape equation like this one is an estimate, not a direct measurement, so pairing it with your waist-to-height ratio is sensible. The BMI and waist-to-height calculator does that.
The US Army itself has moved away from tape equations: since July 2026 it uses a waist-to-height ratio below 0.55 as its only body-composition standard. That limit is an administrative standard for soldiers, not a health target.
Body fat in Bodyvault
When you log your waist, neck and hips, Bodyvault’s measurement sheet works out the same US Navy estimate, which you can save as your body fat or replace with a reading from a scale. The Health tab shows your body fat with lean mass, BMI and waist-to-height ratio next to your weight trend and progress photos, and the coach points out a waist-to-height ratio of 0.5 or more. Once you have a body fat reading, your resting energy is estimated from lean mass with the Katch–McArdle equation instead of a weight-only formula. For a calorie target from your own numbers, see the calorie deficit calculator.
Privacy
The calculation runs in this page. Nothing you type is sent to a server, saved in your browser or put into the address bar; reloading the page restores the example. The site’s usual behaviour is in the privacy policy.
Questions
How accurate is the Navy body fat calculator?
Expect an error of roughly ±3.5 to 6 percentage points for one person. In a 2024 study against DXA scans, it read on average about 4.8 points low in men and 1.7 in women.
What is a healthy body fat percentage?
It depends on age and sex. The body fat matching a healthy BMI is about 21–33% for women and 8–20% for men aged 20–39, rising with age. India’s 2025 revised definition of obesity uses more than 25.5% (men) and 38% (women).
Where do I measure my waist for the Navy method?
Men measure the abdomen at the navel. Women measure the natural waist at its narrowest point and the hips at the widest part of the buttocks. Measure on the skin after a normal breath out.
Why does my smart scale give a different number?
Scales estimate body fat with bioimpedance and their own equations, which have their own errors. Pick one method and follow its trend rather than comparing methods.
Is my data saved?
No. The calculation runs in the page and nothing is sent anywhere.
Sources
- Hodgdon JA (1990). Body composition in the military services: standards and methods. In: Body Composition and Physical Performance: Applications for the Military Services. National Academies Press, pp. 57–70.
- McClung HL et al. (2025). Science behind policy: implementing a modern circumference-based body fat equation with a physical fitness threshold is associated with lower musculoskeletal injury risk. Int J Obes 49(4):723–730.
- Taylor KM et al. (2024). Development and cross-validation of a circumference-based predictive equation to estimate body fat in an active population. Obes Sci Pract 10(2):e747.
- US Army (2019). Army Regulation 600-9, The Army Body Composition Program, Appendix B (measurement procedures).
- US Army (2026). Army Directive 2026-13, Army Body Composition Program and Standards.
- Gallagher D et al. (2000). Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index. Am J Clin Nutr 72(3):694–701.
- Misra A et al. (2025). Revised definition of obesity in Asian Indians living in India. Diabetes Metab Syndr 19(1):102989.
- Rubino F et al. (2025). Definition and diagnostic criteria of clinical obesity. Lancet Diabetes Endocrinol 13(3):221–262.