Body Fat Calculator
Estimate your body fat percentage using the clinically validated U.S. Navy circumference method. Enter your measurements in metric or imperial units to see your fat percentage, fat mass, lean mass, and fitness category.
This calculator provides general estimates for informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider.
How It Works
The U.S. Navy body fat method uses circumference measurements — neck, waist, and (for women) hips — along with height to estimate body fat percentage. It was developed for use in military fitness assessments and is one of the most widely used field methods because it requires only a tape measure.
The formulas (measurements in centimetres):
Male: BF% = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76
Female: BF% = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387
The logarithm compresses the relationship between circumference differences and body fat, reflecting how fat tends to accumulate in certain areas more than others. The formula was calibrated against hydrostatic (underwater) weighing data, the gold standard for body composition testing.
Once BF% is known:
Fat mass (kg) = body weight × (BF% / 100)
Lean mass (kg) = body weight − fat mass
Body fat percentage categories (American College of Sports Medicine):
Men:
- Essential fat: 2–5%
- Athletic: 6–13%
- Fitness: 14–17%
- Acceptable: 18–24%
- Obese: 25%+
Women:
- Essential fat: 10–13%
- Athletic: 14–20%
- Fitness: 21–24%
- Acceptable: 25–31%
- Obese: 32%+
Limitations: The Navy method has a standard error of about 3–4 percentage points compared to DEXA scanning. Accuracy depends heavily on correct measurement technique — measurements should be taken at the same time of day, after exhaling normally, with the tape parallel to the floor.
Frequently Asked Questions
What is body fat percentage?
Body fat percentage is the proportion of your total body weight that is fat mass. The remainder is lean mass — muscle, bone, water, and organs. Unlike BMI, which only accounts for total weight and height, body fat percentage distinguishes between different tissue types and provides a clearer picture of body composition.
How is the Navy method different from BMI?
BMI divides weight by height squared and cannot tell muscle from fat. A muscular 90 kg athlete at 180 cm has the same BMI as an unfit person of the same height and weight. The Navy method uses circumference measurements to estimate the actual fat fraction, so a muscular person will correctly show a lower body fat percentage.
What are healthy body fat ranges?
For men, 14–24% is generally considered healthy (fitness to acceptable range). For women, 21–31% is the healthy range. Essential fat — the minimum needed for physiological function — is 2–5% in men and 10–13% in women. Athletes often carry 6–20% (men) or 14–24% (women).
How do I measure accurately?
Use a flexible, non-stretching tape measure. For waist, measure at the narrowest point, usually at the navel level, after exhaling normally — do not suck in. For neck, measure just below the larynx (Adam's apple). For hips (women), measure at the widest point of the buttocks. Take measurements in the morning before eating. Average two readings if they differ.
Why does it need hip measurement for women but not men?
Women naturally carry more fat in the hips and thighs (gynoid fat distribution), so including the hip measurement improves accuracy for female body composition. Men predominantly store excess fat around the abdomen (android distribution), so waist alone is sufficient.