How is body fat % calculated?
This calculator uses the U.S. Navy circumference method, developed for fitness assessment in the armed forces. It estimates body fat from simple body measurements rather than requiring expensive equipment.
The formula
Men: %BF = 495 / (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
Women: %BF = 495 / (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450
Accuracy
The Navy method has a margin of error of approximately ±3–4%. It's a useful tracker for progress over time, but for precise body composition assessment, DEXA scan or hydrostatic weighing are more accurate.
Frequently asked questions
What is a healthy body fat percentage?
Healthy ranges differ by sex: for women, 21–33% is generally considered healthy (14–20% is athletic). For men, 18–24% is healthy (6–13% is athletic). These ranges shift upward slightly with age. Body fat below essential fat levels (10–13% for women, 2–5% for men) is dangerous.
How accurate is the Navy method for body fat?
The US Navy circumference method is accurate to within approximately ±3–4% for most people. It's less accurate for very lean or very obese individuals. DEXA scanning is the gold standard (±1–2% accuracy) if you need a precise measurement.
Can body fat percentage be too low?
Yes. Extremely low body fat — below essential fat levels — impairs organ function, hormone production, immune function, and bone health. In women, very low body fat causes hormonal disruption and loss of menstrual function. Sustainable athletic body fat (14–20% for women, 6–13% for men) is very different from dangerously low levels.
Is body fat or BMI a better health indicator?
Body fat percentage is generally more informative than BMI because it directly measures fat vs lean mass. BMI can misclassify muscular people as overweight and people who've lost muscle (sarcopenic obesity) as healthy. However, waist circumference — which reflects visceral fat — is often the most clinically useful single measurement.
Not medical advice. Body fat estimates are approximations. Consult a healthcare provider for clinical assessment.