Body Fat Calculator — US Navy Method
Calculate your body fat percentage using the US Navy circumference method. All you need is a tape measure — enter height, neck, and waist (plus hip for women) to see your body fat percentage and fitness category instantly. No signup, runs entirely in your browser.
Measure neck just below the larynx. Measure waist at the navel.
How to Use the Body Fat Calculator
- 1Select your gender and preferred unit (inches or centimetres).
- 2Measure and enter your height, neck circumference (just below the larynx), and waist circumference (at the navel for men, narrowest point for women).
- 3Women also need hip circumference at the widest point — this is required by the Navy formula for female body composition.
- 4Read your body fat percentage and fitness category (Essential fat, Athletic, Fitness, Acceptable, or Obese) instantly.
Body Fat vs BMI
BMI only measures weight relative to height — it cannot distinguish between muscle and fat. A bodybuilder and a sedentary person of the same height and weight have identical BMIs but vastly different body compositions. Body fat percentage is a direct measure of fat mass and is a far more meaningful indicator of cardiovascular risk, athletic fitness, and metabolic health. The Navy method provides a practical estimate using only a tape measure, making it accessible without specialist equipment.
Tips for Accurate Body Fat Measurements
Measure in the morning
Take measurements first thing in the morning before eating or drinking. Abdominal bloating after meals can add 1–2 cm to your waist reading and skew results.
Keep the tape snug, not tight
The tape should touch your skin all the way round without compressing it. Pulling it tight artificially reduces measurements; leaving it loose inflates them. Snug is the correct tension.
Measure after a normal exhale
Take your waist measurement after breathing out normally — not after forcefully sucking in your stomach or after a deep inhale. Relaxed abdominal muscles give the most reproducible reading.
Use the same conditions each time
Track progress by measuring under identical conditions — same time of day, same hydration level, same measurement points. Consistency matters more than precision for trend monitoring.
Round neck measurements up
The Navy formula specifies rounding neck measurements to the nearest 0.5 cm upward. This is a deliberate conservative adjustment — apply it when entering values to stay consistent with the original formula.
Track trends, not individual readings
A single measurement has inherent variability of ±1–2%. Take three readings on three consecutive mornings and average them. A downward trend over weeks is meaningful; a single 0.5% change is noise.
Frequently Asked Questions
How does the US Navy body fat formula work?
The Navy method uses circumference measurements instead of calipers or DEXA scans. For men: %BF = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76. For women: %BF = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387. All measurements in centimetres. The formula was developed by the US Department of Defense and is used as an official military fitness standard.
How accurate is the Navy method?
The Navy method is generally within 3–4 percentage points of DEXA scan results for most people. It is less accurate at the extremes — very lean individuals (under 8% for men) or very high body fat. For general fitness tracking and trend monitoring, the accuracy is more than sufficient. If you need clinical precision, a DEXA scan is the gold standard.
Where exactly should I measure my waist?
For men: measure at the navel (belly button), keeping the tape horizontal and level. For women: measure at the narrowest point of the waist, which is typically just above the navel. Do not pull the tape tight — snug against the skin is correct. Take the measurement after a normal exhale.
Where do I measure my neck?
Measure just below the larynx (Adam's apple), with the tape perpendicular to the long axis of the neck. Keep your head level and look straight ahead. Round up to the nearest 0.5 cm if you are between measurements.
What is a healthy body fat percentage?
For men: 6–13% is athletic, 14–17% is fitness level, 18–24% is acceptable, 25%+ is considered obese. For women: 14–20% is athletic, 21–24% is fitness level, 25–31% is acceptable, 32%+ is considered obese. Women naturally carry more body fat than men due to hormonal and physiological differences.
What is the difference between body fat percentage and BMI?
BMI (Body Mass Index) measures weight relative to height and does not distinguish between muscle and fat. A muscular athlete can have a "high" BMI but healthy body fat. Body fat percentage directly measures what fraction of your mass is fat tissue, making it a more accurate indicator of health and fitness composition.
Does this calculator store my measurements?
No. All calculations run entirely in your browser using JavaScript. Your measurements are never sent to any server and are cleared when you close or refresh the tab.