How to use Body Fat Percentage Calculator
This body fat percentage calculator uses either the US Navy circumference method or the BMI-based estimation to estimate the percentage of your body composed of fat. The US Navy method — measuring waist, neck and (for women) hip circumferences — is widely used and requires no special equipment. Once you have your body-fat percentage, this tool also shows your fat mass versus lean mass split, and classifies you using American Council on Exercise (ACE) categories.
- Choose your gender and preferred method(US Navy or BMI-based).
- Select imperial (inches) or metric (cm) units.
- For US Navy: enter height, waist, neck and (females) hip measurements.
- For BMI method: enter height and weight.
- Optionally enter body weight to see fat mass and lean mass in absolute terms.
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US Navy formula explained
The US Navy method uses logarithms of circumference measurements to estimate body density and thus body fat. For men: 495 / (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450. For women the hip measurement is added. Measure the waist at the narrowest point (navel level for men) and the neck just below the Adam's apple. Accuracy is within ±3–4% for most people, improving with multiple measurements.
ACE body fat categories
The American Council on Exercise defines five categories for men: Essential Fat (2–5%), Athletes (6–13%), Fitness (14–17%), Average (18–24%) and Obese (≥25%). Women carry more essential fat for hormonal function: Essential (10–13%), Athletes (14–20%), Fitness (21–24%), Average (25–31%) and Obese (≥32%). These thresholds help contextualise a number that is hard to interpret in isolation.
| 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% |
Limitations and best practices
All estimation methods carry error. DEXA scanning (±1–2%) and hydrostatic weighing are more accurate but require clinical equipment. Circumference methods can vary by 3–5% depending on measurement consistency. Take measurements first thing in the morning before eating, and use the same tape tension each time. Track trends over 4–8 weeks rather than single readings for a meaningful picture of progress.
Worked examples
Man, waist 90 cm, neck 40 cm, height 178 cm
Inputs: US Navy method, male
Result: ≈ 18.7% body fat
Fat mass and lean mass split
Inputs: 80 kg at 18.7% body fat
Result: ≈ 15.0 kg fat · 65.0 kg lean mass
Glossary
- Essential Fat
- The minimum fat required for physiological function; below this causes serious health risks.
- Lean Mass
- Everything in the body that is not fat: muscle, bone, organs and water.
- DEXA
- Dual-energy X-ray absorptiometry — gold-standard body composition scan.
- Circumference method
- Body fat estimation using tape measurements of specific body sites.
Related reading
Frequently Asked Questions
Why use Body Fat Percentage Calculator?
- Estimate body fat percentage using the US Navy circumference method with only a tape measure
- Calculate absolute fat mass and lean mass in kilograms from a single body-fat reading
- Classify your result against ACE categories to gauge where you fall on the fitness spectrum
- Compare US Navy and BMI-based estimates to identify consistency or flag outliers
Common use cases
- Monitor body composition monthly to track fat loss while preserving lean mass during a cut
- Determine whether you fall in the athletic or fitness ACE category after a training block
- Calculate lean mass as an input for the Katch-McArdle BMR formula
- Assess whether apparent weight gain is lean mass or fat when eating at a strength-training surplus
- Use neck and waist measurements over time to spot visceral fat accumulation trends
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