Body Fat Calculator for Metric and Imperial Units
This calculator accepts both metric (centimeters and kilograms) and imperial (inches and pounds) measurements. When toggling between unit systems, all circumference measurements automatically convert while preserving exact mathematical equivalency.
How the U.S. Navy Body Fat Method Works
Developed by the Naval Health Research Center, the U.S. Navy tape measure method uses logarithmic transformations of circumference ratios to estimate body density. By comparing abdominal fat storage sites against neck circumference and height, it provides a widely validated, non-invasive estimate of body fat percentage.
How to Measure Waist, Neck, and Hips
For reliable results, use a flexible, non-stretch tape measure and ensure the tape is level around the body without pulling tight:
- Neck Circumference: Measure around the neck just below the larynx (Adam’s apple), keeping the tape level and relaxed.
- Waist Circumference (Men): Measure horizontally around the abdomen at the level of the navel (belly button).
- Waist Circumference (Women): Measure around the narrowest point of the natural waistline (above the navel, below the ribcage).
- Hip Circumference (Women): Measure around the widest part of the hips and buttocks.
Note: Measurement protocols can vary slightly between clinical guidelines. Measuring consistently at the same landmarks improves tracking accuracy.
Body Fat Percentage Formula for Men
All measurements are converted to inches before applying the logarithmic equation.
Body Fat Percentage Formula for Women
Women’s formula incorporates hip circumference to account for gynoid fat distribution patterns.
Understanding Body-Fat Estimates
Body fat percentage estimates provide a snapshot of body composition. Essential fat is required for basic physiological processes (such as hormone production and organ insulation). Additional body fat varies across individuals based on genetics, activity level, and age.
Limitations of Body Fat Calculators
Body-fat calculators estimate body composition from measurements; they do not directly measure body fat. Results can vary with measuring technique, hydration, body shape, muscle mass, age, pregnancy, and the calculation method. DEXA, skinfold measurements, and hydrostatic weighing also have inherent limitations.
Using Body-Composition Estimates Safely
Body-fat percentage is not a measure of worth, attractiveness, or overall health. If tracking body measurements or weight causes distress, anxiety, compulsive behavior, or affects your relationship with eating or exercise, consider stepping away from tracking and seeking support from a qualified professional.
Do not use this calculator during pregnancy. Discuss any body composition questions with a qualified healthcare provider.
Public Health Sources & Citations
- Hodgdon, J. A., & Beckett, M. B. (1984). Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center, Report No. 84-29 / 84-11.
- Centers for Disease Control and Prevention (CDC). Assessing Your Weight and Body Composition. Available at: cdc.gov/healthyweight