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Body fat calculator: estimate your body fat percentage
The US Navy circumference method estimates your body fat from neck, waist and (for women) hip measurements — no calipers or lab equipment required.
Body fat calculator
Your result
Lean mass
60.3 kg
Fat mass
14.7 kg
About this tool
What the body fat calculator measures — and who it's for
The US Navy circumference method estimates body fat percentage from neck, waist and (for women) hip measurements. It was developed by the US military for large-scale fitness assessments and is one of the most accurate field methods that doesn't require calipers or expensive equipment.
Results fall into five categories defined by the American Council on Exercise (ACE): essential fat, athletes, fitness, acceptable, and obese — giving more nuance than BMI's weight-only assessment.
Step by step
How to use the body fat calculator
- 1
Choose metric or imperial units
Pick whichever system your tape measure uses.
- 2
Enter your neck and waist measurements (men), or neck, waist and hip (women)
Use a flexible tape pulled snug but not tight. Measure each site twice and average the readings.
- 3
Enter your height and weight
These are needed to calculate your lean and fat mass in kilograms.
- 4
Press Calculate
Your body fat percentage, category and mass breakdown appear instantly.
Methodology
The formula behind your result
Male
86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76
Female
163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387
All measurements in centimetres.
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Acceptable | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
Source: American Council on Exercise (ACE) body fat percentage categories.
Worked example
Example calculation
A 35-year-old man, 178 cm tall, with a waist of 85 cm and neck of 37 cm. log₁₀(85 − 37) = log₁₀(48) ≈ 1.681; log₁₀(178) ≈ 2.250. Result: 86.010 × 1.681 − 70.041 × 2.250 + 36.76 ≈ 16.5% — in the Fitness category.
Be aware
Assumptions and limitations
- Less accurate than DEXA or hydrostatic weighing.
- Assumes fat distribution follows population averages.
- Requires accurate measurements — use a flexible tape measure pulled snug but not tight.
- Not validated for children, pregnant women, or people with lymphedema.
Questions
Frequently asked questions
Is the Navy method accurate?
It has a margin of error of ±3–4%, which is acceptable for general fitness tracking. Athletes with unusual fat distribution may get less accurate results.
What is a healthy body fat percentage?
For men: 14–17% fitness, 18–24% acceptable. For women: 21–24% fitness, 25–31% acceptable. Athletes sit below these ranges.
How do I measure my waist and neck?
Waist: measure horizontally at the navel (men) or narrowest point (women). Neck: measure below the larynx (Adam's apple), perpendicular to the long axis.
Why does sex affect the formula?
Women naturally carry more essential fat (10–13% vs 2–5% for men) due to hormonal and reproductive physiology. The formula accounts for this difference.
What body fat percentage is considered healthy?
According to the American Council on Exercise (ACE): for men, essential fat is 2–5%, athletes 6–13%, fitness 14–17%, acceptable 18–24%, and obese 25% and above. For women: essential fat 10–13%, athletes 14–20%, fitness 21–24%, acceptable 25–31%, and obese 32% and above. These ranges reflect sex-based differences in essential fat required for normal physiological function.
How does body fat percentage differ from BMI?
BMI uses only height and weight and cannot distinguish muscle from fat. Body fat percentage directly estimates the proportion of your body that is fat tissue, making it more informative for body composition assessment. A muscular person can have a high BMI but a low body fat percentage — the body fat calculator captures this; BMI does not.
Can I reduce body fat in a specific area?
No — spot reduction is a myth. When you create a calorie deficit, your body draws on fat stores from throughout the body according to genetics and hormonal patterns, not from the area you exercise most. Consistent aerobic exercise combined with a calorie deficit reduces total body fat; resistance training preserves lean mass during fat loss, which improves your body fat percentage over time.
How often should I measure my body fat?
Every 4–6 weeks is a reasonable interval for tracking changes. More frequent measurements are dominated by day-to-day fluid fluctuation rather than actual fat changes. Measure in consistent conditions — same time of day, same hydration state, same technique — to reduce noise in your readings.
Estimates, not medical advice
FitnessCalculator.info provides general health information for educational purposes only and does not replace advice from a qualified doctor or registered dietitian.