Body fat calculator (US Navy method)
Estimate your body fat percentage with a tape measure, using the US Navy formula, and compare it with healthy ranges for your age and sex. Works in lb or kg.
How to measure
Use a flexible tape measure. Measure each spot two or three times and use the average.
- Height: without shoes, standing straight.
- Neck: just below the Adam’s apple (the bump at the front of the throat).
- Waist: men at the navel; women at the narrowest point.
- Hips (women only): around the widest part of the bottom.
- Weight (optional): splits your weight into fat and everything else, and links to your FFMI.
Measure at the same time of day each time, ideally in the morning before eating, so changes are real and not just a big lunch.
How it works
The US Navy method predicts body fat from a few tape measurements and your height. Hodgdon and Beckett built it at the Naval Health Research Center by comparing measurements with underwater weighing [1]. With everything in inches:
- Men: 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76
- Women: 163.205 × log₁₀(waist + hips − neck) − 97.684 × log₁₀(height) − 78.387
The US military used these equations to check body composition for decades [2].
How accurate is it?
In a 2022 study of US Marines, the tape method read about 2.5 points lower than a DEXA scan for men and 1–2 points higher for women, on average [2]. It still put about 92% of Marines in the same category as the scan [3].
So treat the number as an estimate and the trend as the real result. Measure every 2–4 weeks the same way. If your waist is shrinking while your lifts go up, you’re losing fat and keeping muscle.
Healthy ranges
These ranges come from a study that matched body fat to BMI ranges across ages [4]:
| Age | Men | Women |
|---|---|---|
| 20–39 | 8–19% | 21–32% |
| 40–59 | 11–21% | 23–33% |
| 60–79 | 13–24% | 24–35% |
The calculator also shows whether you’re below the range, or in the overweight or obese range for your age.
What to do with it
- Want to lose fat? See the fat loss goal: eat a little less, keep protein high, and keep lifting.
- Want to build muscle? See the muscle goal, and use FFMI to see how much muscle you carry for your height.
Questions
How accurate is the US Navy body fat calculator?
Close enough to track progress. Compared with a DEXA scan it reads about 2–3 points low for men and 1–2 points high for women on average, and it puts about 9 in 10 people in the right category. Use the same tape, the same spots and the same time of day, and watch the trend.
Where do I measure my waist?
Men: around the belly at the navel. Women: at the narrowest point of the waist. Keep the tape level and snug without pressing in, and measure after a normal breath out.
What is a healthy body fat percentage?
For adults aged 20–39, about 8–19% for men and 21–32% for women. The healthy range rises a few points with age: 11–21% and 23–33% at 40–59, and 13–24% and 24–35% at 60–79.
Does it work if I lift weights and carry a lot of muscle?
Better than BMI does. BMI only knows your height and weight, so muscle counts against you. The Navy method uses your waist and neck instead. A very thick neck from training can make the result read slightly low.
General information, not medical advice. If you have a health condition, are pregnant or take medication, check with your doctor.
Sources
- [1]Hodgdon and Beckett, Prediction of percent body fat for U.S. Navy men from body circumferences and height, Naval Health Research Center Report 84-11 (1984). https://apps.dtic.mil/sti/citations/ADA143890
- [2]Potter et al., Circumference-Based Predictions of Body Fat Revisited: Preliminary Results From a US Marine Corps Body Composition Survey, Frontiers in Physiology (2022). https://pmc.ncbi.nlm.nih.gov/articles/PMC9008774/
- [3]Human Performance Resource Center, How the Military Measures Body Composition. https://www.hprc-online.org/physical-fitness/training-performance/how-military-measures-body-composition
- [4]Gallagher et al., Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index, American Journal of Clinical Nutrition (2000). https://doi.org/10.1093/ajcn/72.3.694