Body fat calculator
Estimate your body fat percentage using the US Navy circumference method. Includes body fat category, fat mass and lean mass for men and women.
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What body fat percentage means
Body fat percentage is the proportion of your total weight that comes from fat tissue, as opposed to lean tissue (muscle, bone, organs, water). Two people of the same weight and height can have very different body compositions — which is why body fat percentage often gives a clearer picture of health than BMI alone.
Different levels of body fat serve different purposes. Essential fat (the minimum needed for healthy function) is around 2–5% for men and 10–13% for women. Athletic, fitness and acceptable ranges span above that. Carrying too little or too much body fat both carry health risks, so knowing where you fall helps you set informed goals.
US Navy method explained
The US Navy body fat formula is one of the most widely used circumference-based methods. It uses height and neck circumference for everyone, plus waist for men and waist plus hip for women. The formula estimates body density, then converts it to a body fat percentage using the Siri equation.
- For men: 86.01 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76
- For women: 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387
The accuracy depends heavily on your measurements. Use a flexible tape measure, keep it level and snug against the skin, and measure at the narrowest point for the waist (just above the belly button) and the widest point for the hips. The neck is measured just below the larynx.
Worked example: male, 175cm, 38cm neck, 85cm waist
The formula coefficients are calibrated for inches, so measurements are converted first: 175cm = 68.9in, 38cm neck = 15.0in, 85cm waist = 33.5in.
- Step 1: waist − neck = 33.5 − 15.0 = 18.5in
- Step 2: 86.01 × log₁₀(18.5) = 86.01 × 1.267 = 108.98
- Step 3: 70.041 × log₁₀(68.9) = 70.041 × 1.838 = 128.74
- Result: 108.98 − 128.74 + 36.76 = 17.0% body fat — "Athletic" category
For a female example — 165cm height, 32cm neck, 70cm waist, 95cm hip — the same conversion-then-formula process gives 25.1% body fat, in the "Fitness" category.
Body fat by waist size
Male estimates at a fixed 175cm height and 38cm neck, waist varying — shows how sensitive the result is to waist measurement specifically.
| Waist | Estimated body fat | Category |
|---|---|---|
| 75 cm | 8.1% | Athletic |
| 80 cm | 12.8% | Athletic |
| 85 cm | 17.0% | Fitness |
| 90 cm | 20.8% | Acceptable |
| 95 cm | 24.2% | Acceptable |
| 100 cm | 27.4% | Obese |
A 25cm difference in waist size alone (75cm → 100cm) shifts the estimate by roughly 19 percentage points — waist is by far the most influential measurement in this formula, so measure it carefully.
Healthy ranges by age and gender
- Men — Essential: 2–5% | Athletic: 6–13% | Fitness: 14–17% | Acceptable: 18–24% | Obese: 25%+
- Women — Essential: 10–13% | Athletic: 14–20% | Fitness: 21–24% | Acceptable: 25–31% | Obese: 32%+
These are general guidelines from the American Council on Exercise (ACE). Your age, genetics, activity level and personal health history all influence what is optimal for you. Body fat also tends to increase naturally with age, so do not compare yourself to elite athletes or fitness models.
What this calculator does not include
- Direct fat measurement — this is a circumference-based estimate, not a direct measurement like a DEXA scan, hydrostatic weighing or skinfold calipers, all of which are more accurate but require special equipment.
- Body fat distribution — the result is a single overall percentage; it doesn't distinguish visceral (around organs, higher health risk) from subcutaneous (under skin) fat.
- Measurement error — a loose or crooked tape measure can shift the result by several percentage points, especially at the waist (see the table above).
Frequently asked questions
What is a healthy body fat percentage?
For men, 6–24% is generally healthy depending on age; for women, 14–31%. Athletic ranges (6–13% men, 14–20% women) are sustainable for active individuals.
How accurate is this calculator?
The US Navy method has a margin of error of about 2–4% compared to DEXA scans. Accuracy depends on taking measurements correctly.
What is the US Navy method?
It uses circumference measurements (neck, waist, hips for women) and height to estimate body density, then converts it to body fat percentage using well-established equations.
How do I measure my waist correctly?
Measure around your bare abdomen at the narrowest point, typically just above your belly button. Keep the tape snug but not tight, and parallel to the floor.
Is the US Navy method more accurate than BMI for body composition?
Yes, generally — BMI can't distinguish muscle from fat, while the US Navy method at least estimates body density from circumference measurements. Neither replaces a DEXA scan, but the Navy method gives a more body-composition-aware estimate than BMI alone. See our BMI vs body fat comparison.
This tool is for information only and is not medical advice. Consult a health professional for accurate body composition assessment.