U.S. Navy body fat formula
All measurements are in inches:
Women: %BF = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387
Fat mass = weight × %BF ÷ 100, and lean mass = weight − fat mass.
Body fat categories (ACE)
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25% + | 32% + |
Tips for consistent results
- Measure in the morning, before eating, with a flexible non-stretch tape.
- Take each measurement three times and use the average.
- Track the trend every 2–4 weeks rather than day to day.
Compare with your BMI, which uses only height and weight.
How to use the calculator
- Choose your sex and units, then enter your height.
- Measure your neck just below the larynx (Adam’s apple), with the tape sloping slightly downward to the front.
- Men: measure the waist horizontally at the navel. Women: measure the waist at its narrowest point and the hips at their widest.
- Read your body fat percentage, category, fat mass and lean mass.
How accurate is the Navy method?
The U.S. Navy circumference method was developed by Hodgdon and Beckett in 1984 and validated against underwater weighing. Studies typically find it within about 3–4 percentage points of laboratory methods for most people, which is similar to many consumer devices. It can underestimate fat in people who carry fat mainly on the hips and thighs (for men) and overestimate it in people with very thick necks from strength training.
Other ways to measure body fat
- DEXA scan: X-ray based, often considered the clinical reference; also shows bone density and where fat is stored.
- Hydrostatic (underwater) weighing and air displacement (Bod Pod): accurate lab methods, less widely available.
- Skinfold calipers: accurate in trained hands using a standard protocol, less so when self-measured.
- Bioelectrical impedance (smart scales, handheld devices): convenient but strongly affected by hydration, food and exercise; best used for trends under the same conditions.
Body fat and health
Some fat is essential: about 2–5% for men and 10–13% for women, for hormones, organs and, in women, reproduction. Very low body fat can disrupt hormones and menstrual cycles and weaken bones. At the other end, high body fat — especially around the abdomen — is linked to type 2 diabetes, heart disease, fatty liver and some cancers. Because where fat is stored matters, pair your result with your waist-to-height ratio.
Lowering body fat
- A moderate calorie deficit of about 300–500 kcal a day leads to steady loss of roughly 0.5–1% of body weight per week.
- Strength training two to three times a week and adequate protein (about 1.6 g per kg of body weight) help keep muscle while losing fat.
- Re-measure every 2–4 weeks; daily changes are mostly water.