Body Fat Calculator
Estimate your body fat percentage using the US Navy method with simple body measurements. More accessible than DEXA scans for everyday tracking.
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Formula
US Navy Method (Hodgdon & Beckett, 1984)
For men: 495 ÷ (1.0324 − 0.19077×log(waist−neck) + 0.15456×log(height)) − 450. For women, hip circumference is added. All measurements in cm. This method uses body circumferences as a proxy for body density, then estimates fat percentage.
How to use the Body Fat Calculator
- 1
Enter your sex
- 2
Enter your height
Value should be in cm.
- 3
Enter your waist circumference
Measure at navel level
- 4
Enter your neck circumference
Measure below the larynx
- 5
Enter your hip circumference (women)
Measure at widest point
- 6
Read your results instantly
Results update in real time as you type.
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How to measure accurately
Consistent measurement technique is essential for tracking progress. Measure the waist at the level of the navel, standing relaxed (not sucked in). For the neck, measure just below the larynx. For women, measure hips at the widest point, feet together.
Measure first thing in the morning, before eating or drinking, for the most consistent results. Take 2–3 measurements and use the average. Use a flexible tape measure pulled snug but not compressing the skin.
Body fat categories by sex
Essential fat (minimum for physiological function): 2–5% men, 10–13% women. Athletic: 6–13% men, 14–20% women. Fitness: 14–17% men, 21–24% women. Acceptable/average: 18–24% men, 25–31% women. Obese: 25%+ men, 32%+ women.
Note these differ substantially from BMI categories — a muscular person may be classified as 'overweight' by BMI while having body fat in the 'athletic' range.
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Accuracy limitations
The US Navy method has a standard error of about 3–4 percentage points. This means a result of 18% body fat might actually be 14–22%. It's best used for tracking change over time (where relative accuracy matters) rather than for absolute body composition diagnosis.
For higher accuracy, consider DEXA scanning (~1–2% error), which is increasingly available at gyms and clinics for $30–100, or hydrostatic weighing.
Tips & Insights
Track change, not absolute number
Given the ~3-4% margin of error, focus on whether your number is trending down over weeks and months, not the precise value on any given day.
Waist-to-height ratio is simpler and powerful
Research supports waist ÷ height as a strong predictor of cardiometabolic risk. A ratio below 0.5 (waist less than half your height) is the general target for good metabolic health.
Worked Examples
Male measurement
Estimated body fat: approximately 19.2% — in the acceptable/average range for men (18–24%). Goal range for fitness level would be 14–17%.
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Frequently Asked Questions
What is a healthy body fat percentage?
Healthy ranges vary by sex: Men: Essential fat 2-5%, Athletes 6-13%, Fitness 14-17%, Acceptable 18-24%. Women: Essential 10-13%, Athletes 14-20%, Fitness 21-24%, Acceptable 25-31%.
How is body fat different from BMI?
BMI uses only height and weight and can't distinguish muscle from fat. Body fat percentage directly estimates the proportion of fat mass in your body, giving a clearer picture of composition.
What's the most accurate way to measure body fat?
DEXA (dual-energy X-ray absorptiometry) is the most accessible highly accurate method (~1-2% error). Hydrostatic weighing and Bod Pod are similarly accurate. Bioelectrical impedance (home scales) is convenient but less accurate (±3-5%).
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