Free Tool · Body Composition
Body Fat Calculator
Estimate your body fat percentage with the US Navy method. The Hodgdon-Beckett equation uses neck, waist, and (for women) hip circumferences plus height. It is the most reproducible body-fat estimate you can run yourself at home.
How it works
The Hodgdon-Beckett equation
The US Navy adopted this circumference-based formula in 1984 to assess body composition for fitness standards. It uses log-transformed differences between waist, neck, and (for women) hip circumferences, scaled by height.
For men: %BF = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76. For women: %BF = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387. All measurements in centimeters; the calculator handles unit conversion automatically.
Compared to bioelectrical impedance scales (BIA), the Navy method is more reliable across hydration states. Compared to skinfold calipers, it is far more reproducible without a trained measurer.
Reference ranges
Body-fat classifications
| Classification | Men | Women |
|---|---|---|
| Essential fat | 2-5% | 10-13% |
| Athletic | 6-13% | 14-20% |
| Fitness | 14-17% | 21-24% |
| Average | 18-24% | 25-31% |
| Above average | 25%+ | 32%+ |
Source: American Council on Exercise (ACE) and ACSM guidelines.
Frequently asked questions
Questions we hear a lot
The US Navy method, formally the Hodgdon-Beckett equation, estimates body fat from circumference measurements: neck and waist for men, plus hip for women. It was developed for Navy fitness assessments and is one of the most accurate non-laboratory methods because it captures both fat distribution and frame size.
Studies show the Navy method estimates within 3 to 4 percentage points of DEXA for most adults. Accuracy is best for people with average to moderately above-average body fat. Highly muscular athletes and people with very high body fat sit at the edges of the formula's calibration data.
For men, measure at the navel. For women, measure at the narrowest point of the torso, typically just above the navel. Stand naturally, do not suck in, and pull the tape snug without compressing the skin. Take the measurement at the end of a normal exhale.
Just below the larynx (Adam's apple), with the tape angled slightly forward to follow the natural slope of the neck. Keep your head straight and shoulders relaxed. The neck circumference is the smallest of the three measurements and most sensitive to technique.
Women carry a larger fraction of body fat in the hips and lower body, and the Navy formula was originally calibrated to account for that pattern. Skip the hip measurement and the result systematically underestimates female body fat by 3 to 6 points.
Skinfold calipers (Jackson-Pollock 3-site or 7-site) are slightly more accurate when an experienced practitioner takes the measurements, but the technique is hard to learn and inter-rater reliability is poor. The Navy method is more reproducible by yourself at home, which makes it more useful for trend tracking even if a single skinfold measurement is more accurate at one moment.