How to use the body fat calculator
- US Navy tape method: measure your height, waist and neck (and hips for women) with a soft tape. The method was developed by the US Navy and was long used across the US military (the US Army moved to a waist-only tape test in 2023).
- From BMI and age: a quicker but rougher estimate from your height, weight and age.
Add your weight to see your fat mass and lean mass.
Formulas
Men (US Navy, inches): 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76
Women (US Navy, inches): 163.205 × log₁₀(waist + hips − neck) − 97.684 × log₁₀(height) − 78.387
From BMI (Deurenberg): 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4 (sex = 1 for men, 0 for women)
Metric measurements are converted to inches exactly (1 in = 2.54 cm) before using the Navy formulas.
Worked example
A man 180 cm tall, waist 90 cm, neck 38 cm: in inches that's 70.87, 35.43 and 14.96.
86.010 × log₁₀(20.47) − 70.041 × log₁₀(70.87) + 36.76 = 19.9% body fat, in the "average" range. At 80 kg, that's about 15.9 kg of fat and 64.1 kg of lean mass.
Body fat categories
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5.9% | 10–13.9% |
| Athletes | 6–13.9% | 14–20.9% |
| Fitness | 14–17.9% | 21–24.9% |
| Average | 18–24.9% | 25–31.9% |
| Obese | 25% or more | 32% or more |
Categories from the American Council on Exercise, using your result to 1 decimal place. A result for a woman under 10% is below essential fat, so check the measurements. Compare with the BMI calculator.
Frequently asked questions
How accurate is the tape method?
Usually within a few percentage points of lab methods such as DEXA scans, if you measure carefully. Measure at the same time of day and take the average of two readings.
Why can BMI-based body fat be wrong?
BMI doesn't know how much of your weight is muscle, so very muscular people can get a body fat estimate that's far too high.
Sources
- Hodgdon & Beckett (1984), Naval Health Research Center reports 84-11 and 84-29
- Deurenberg et al. (1991), British Journal of Nutrition
- American Council on Exercise
Formulas checked 29 October 2026. How we test our calculators. This calculator gives general estimates for adults and is not medical advice. Talk to a doctor or dietitian about your own health.