Body Fat Calculator
Estimate body fat percentage using the US Navy method
What is it?
This calculator estimates body fat percentage using the U.S. Navy method, which uses simple circumference measurements (neck, waist, and for women, hips) along with height to estimate body composition without specialized equipment.
Formula
Men: 495 / (1.0324 − 0.19077×log10(waist−neck) + 0.15456×log10(height)) − 450
Women: 495 / (1.29579 − 0.35004×log10(waist+hip−neck) + 0.221×log10(height)) − 450
Formula Explanation
The Navy method uses circumference measurements as a proxy for body density, since waist size (adjusted for neck and, for women, hip) correlates with body fat while height accounts for overall body size. It requires no special equipment, trading some precision for convenience compared to methods like DEXA scans or hydrostatic weighing.
Example Calculation
A man with a 90 cm waist, 38 cm neck, and 178 cm height has an estimated body fat of roughly 18.5%, which falls in the "Average" range.
How to Use
- Select your gender and unit system (metric or imperial).
- Enter your height, neck, and waist measurements (plus hip for women).
- Click Calculate Body Fat.
- View your estimated body fat percentage and range.
Benefits
- Requires only a measuring tape — no scales, calipers, or scans needed.
- Gives a reasonable estimate for tracking body composition changes over time.
- Free and quick to redo periodically to track trends.
Use Cases
- Tracking body composition changes alongside a fitness or nutrition plan.
- Getting a rough estimate when specialized equipment (DEXA, calipers) isn't available.
- Comparing progress month to month using consistent measurement technique.
What Your Result Means
Your result places you in a range from Essential fat (the minimum needed for basic physiological function) through Athlete, Fitness, Average, and High. These bands broadly indicate body composition, not overall health — someone in the "Average" range can still be perfectly healthy.
Tips
- Measure at the same time of day and same body position for consistent tracking.
- Keep the tape snug but not compressing the skin, and measure twice to confirm.
- Track the trend over weeks/months rather than reacting to one measurement.
Common Mistakes
- Measuring waist above or below the correct point, which skews results significantly.
- Mixing metric and imperial units without switching the selector.
- Comparing results to another method (like a scale's built-in estimate) and expecting an exact match.
FAQs
How accurate is the U.S. Navy method?
It's a widely used estimation method with reasonable accuracy for most people, though it can be less precise for very lean or very large individuals compared to methods like DEXA scans.
Where do I measure my neck and waist?
Measure your neck just below the larynx (Adam's apple) and your waist at the narrowest point, keeping the tape level and snug but not tight.
What is a healthy body fat percentage?
Healthy ranges vary by gender and age, but roughly 14-24% for men and 21-31% for women is considered the "fitness" to "average" range.
Why do men and women use different formulas?
Women naturally carry more essential fat than men and store it differently, so the formula adds a hip measurement and uses different constants to account for this.
Can this replace a DEXA scan or caliper test?
No — those methods are generally more precise. The Navy method is a convenient, equipment-free estimate best used for tracking relative change over time.
Why did my result change even though my weight stayed the same?
Body fat percentage reflects body composition, not just weight — you can lose fat and gain muscle at a stable weight, which this method can pick up through circumference changes.
Is very low body fat healthy?
No — falling below the essential fat range (roughly under 6% for men, 14% for women) can impair hormone function and overall health, even though it may look lean.
How often should I re-measure?
Every 2-4 weeks is usually enough to see a meaningful trend, since body composition changes gradually.
References
This tool is for educational purposes only. Not a medical diagnosis.
Last updated: July 25, 2026