How this calculator works
Circumference equations infer body composition from the relationship between specific tape measurements and height. They are accessible and more informative than weight alone, but they still estimate rather than directly measure body fat.
Technique matters: a different tape position, breath phase or tension can shift the result. The most useful approach is to repeat measurements under the same conditions and watch the longer trend.
The sex-specific equations combine height with neck, waist and—where applicable—hip circumference. Measurements are converted to inches before the logarithmic formula is applied.
How to use the result
Avoid treating tenths of a percentage point as real change. Even clinical methods disagree, and a home tape estimate has wider error. Compare results monthly, not daily.
Lean mass here means total weight minus estimated fat mass. It includes muscle, bone, organs and water; it is not the same as skeletal muscle mass.
Get a more reliable result
Use a non-stretch tape on bare skin. Keep it horizontal and snug without compressing tissue; measure after a normal exhale. Follow the calculator’s sex-specific landmarks and repeat each site two or three times. If readings differ by more than about 1 cm, reposition and measure again before using the average.
Common errors that change the answer
- Measuring the waistband rather than the specified anatomical landmark.
- Pulling the tape tighter as progress is expected, creating an artificial improvement.
- Comparing this equation directly with a smart scale, calipers or DEXA as if methods were interchangeable.
What to do next
- Measure on bare skin after a normal exhale, without compressing it.
- Use the same tape, time of day and anatomical landmarks each time.
- Track waist and body weight alongside the percentage estimate.
Guides that support this calculator
Frequently asked questions
How accurate is the Navy method?
Accuracy varies by body shape and measurement technique. It is best used for consistent trend tracking, not as a clinical-grade absolute value.
Why does the result change after one centimetre?
The formula uses differences between circumferences, so a small tape change can be amplified. Repeat each site two or three times.
Is a smart scale better?
Consumer bioimpedance scales also estimate and are sensitive to hydration. Whichever method you use, standardise conditions and follow trends.