Body Fat Calculator
Estimate body fat percentage with the US Navy tape-measure method, with correct category ranges for men and women, plus fat mass and lean mass.
The US Navy formulas
Men: %fat = 495 / (1.0324 − 0.19077·log₁₀(waist − neck) + 0.15456·log₁₀(height)) − 450
Women: %fat = 495 / (1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.22100·log₁₀(height)) − 450
All measurements in centimetres. Women include hips because female fat distribution differs from male.
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%+ |
Worked example
A man, 170 cm tall, neck 37 cm, waist 85 cm: waist − neck = 48.
%fat = 495 / (1.0324 − 0.19077·log₁₀48 + 0.15456·log₁₀170) − 450 ≈ 18.5% — the "average" band.
At 70 kg that's about 13 kg of fat mass and 57 kg lean.
Limitations
Tape methods estimate — hydration, measurement position and individual build shift results a few percent.
Track the trend with consistent morning measurements rather than obsessing over a single reading.
Frequently asked questions
How does the US Navy method work?
It estimates body fat from circumference measurements — neck, waist (and hips for women) — combined with height, using log-based formulas the US Navy validated against underwater weighing. It is accurate to roughly ±3–4% for most people.
What is a healthy body fat percentage?
Typical ACE ranges: for men, 6–13% (athletes), 14–17% (fitness), 18–24% (average), 25%+ obese; for women, 14–20% (athletes), 21–24% (fitness), 25–31% (average), 32%+ obese. Women naturally carry more essential fat than men.
How do I measure correctly?
Use a flexible tape, snug but not compressing the skin. Neck: just below the larynx, sloping slightly down at the front. Waist: for men at navel level, for women at the narrowest point. Hips (women): at the widest point. Measure in the morning, before eating.
Why do I get an error saying waist must be larger than neck?
The formula takes the logarithm of (waist − neck), which must be positive — for everyone, the waist circumference is larger than the neck circumference. An error usually means the two measurements were swapped or taken in different units.
Is this more accurate than BMI?
It measures something different and usually more useful: BMI only relates weight to height, while this estimates actual fat percentage, so a muscular person is not misclassified. DEXA scans remain the accuracy gold standard.
This tool provides general health information, not medical advice. Consult a healthcare professional before making decisions based on it.