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Body Fat Calculator

Estimate body fat percentage using the U.S. Navy circumference method.

Sex
Units

Result

Estimated Body Fat
18.3%
403020100Body Fat %: 4Body Fat %: 10Body Fat %: 16Body Fat %: 21Body Fat %: 28Body Fat %: 18EssentialAthleticFitnessAverageObeseYou

About the Body Fat Calculator

Body fat percentage tells you more about your body composition than weight or BMI alone, since it separates fat mass from muscle, bone, and water. Our Body Fat Calculator uses the U.S. Navy circumference method, a well-established estimation technique that only requires a tape measure.

How It Works

The U.S. Navy method estimates body fat percentage from a handful of circumference measurements - neck, waist, and (for women) hips - combined with height. It uses logarithms of these measurements in a formula validated against more expensive methods like hydrostatic weighing, making it one of the more practical at-home estimation techniques available.

Men: %BF = 495 / (1.0324 − 0.19077×log10(waist−neck) + 0.15456×log10(height)) − 450 Women: %BF = 495 / (1.29579 − 0.35004×log10(waist+hip−neck) + 0.22100×log10(height)) − 450

Formula & Methodology

This formula was developed by the U.S. Navy in the 1980s as a practical alternative to hydrostatic (underwater) weighing, the body-fat measurement gold standard at the time, and was statistically fit to correlate circumference measurements with directly measured body density. The logarithmic structure and specific coefficients came from regression analysis against that reference data - waist circumference minus neck circumference (for men) captures abdominal fat relative to a leaner reference point on the body, while the additional hip measurement for women accounts for typically different fat distribution patterns between sexes.

Step-by-Step: Calculating It By Hand

  1. 1Measure neck circumference just below the larynx, and waist circumference at the navel (for women, also measure hip circumference at the widest point).
  2. 2Take the base-10 logarithm of (waist minus neck) for men, or (waist plus hip minus neck) for women.
  3. 3Take the base-10 logarithm of height.
  4. 4Plug those logarithms into the sex-specific formula to solve for estimated body fat percentage.

Examples

Male example

A man with a 15" neck, 34" waist, and 68" height gets an estimated body fat percentage in the mid-teens - typical of an active, fit individual.

Measurement matters

A waist measurement taken too loosely or too high above the navel can shift the result by several percentage points, so consistent technique matters.

Advantages

  • Only requires a tape measure - no special equipment needed
  • Validated method used by the U.S. Navy for decades
  • More informative than BMI for understanding actual body composition
  • Useful for tracking body composition changes over time, not just weight

Common Mistakes

  • Measuring waist and neck inconsistently between sessions
  • Not measuring at the same time of day, which can affect results slightly
  • Treating the estimate as lab-grade precise rather than a solid approximation
  • Comparing results between very different measurement techniques (like calipers vs. this method)

Edge Cases to Watch For

  • Measurement consistency matters enormously here - a waist measurement taken an inch higher or lower, or with different tape tension, can shift the result by several percentage points.
  • This formula was validated primarily on military populations and can be somewhat less accurate for body types outside that reference group, including very lean or very heavy individuals.
  • The Navy method typically has an error margin of a few percentage points compared to more precise methods like DEXA scanning, making it best suited for tracking trends over time rather than treating any single reading as exact.
  • Measuring at a consistent time of day (bloating and hydration affect waist measurement) improves the reliability of tracking changes over multiple sessions.

Common Use Cases

  • Tracking body composition changes during a fitness program
  • Getting a more complete picture than BMI provides
  • Setting realistic body composition goals
  • Checking progress alongside weight and strength measurements
Written & fact-checked by the Calculateus TeamLast updated August 5, 2026How we verify our formulas

Frequently asked questions

How accurate is the Navy circumference method?

It's typically within 3-4% of body fat measured by DEXA scan for most people - accurate enough to track trends, but not a medical-grade measurement.

Where exactly should I measure my waist and neck?

Measure your neck just below the larynx, and your waist at the narrowest point (for men) or at the belly button level (for women), keeping the tape snug but not compressing the skin.

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Conclusion

Body fat percentage, tracked consistently over time using the same method, is one of the more useful numbers for judging real fitness progress. Use this calculator every few weeks with careful, consistent measurements, and pair it with our Lean Body Mass and Ideal Weight calculators for additional context.

References