How the circumference estimate works
The U.S. Navy method combines logarithms of circumferences and height. For the displayed male measurements, the waist-minus-neck value is 47 cm; with 175 cm height the formula returns roughly 17.0%. The result is an estimate derived from tape measurements, not a reading of fat tissue.
Measure the same way
A tape pulled tight, held at a different level, or measured after a large meal changes the input before any formula is used. Keep the tape horizontal and use the same anatomical landmarks each time. For the female equation, hip circumference is an additional measurement and cannot be omitted or substituted with a clothing size.
Population model assumptions
The equation was fitted to population measurements. It assumes the relationship between external girths and body composition is close enough for an estimate, but body shape, age, ethnicity, muscle development, and fluid retention can change that relationship. Two people with matching tape values need not have matching body composition.
Limits of a percentage
This page cannot assess nutritional status, hormone conditions, athletic readiness, or disease risk. A percentage is especially easy to overread when it is close to a chart boundary. Discuss a concerning change, eating difficulty, or health symptom with an appropriate health professional instead of chasing repeated tape readings.
A useful comparison record
For progress tracking, record the date, sex equation used, and every circumference in centimetres. A weekly series taken at the same time and posture says more than a comparison between one home measurement and a different device at a gym.
Check the arithmetic in context
Take two or three tape readings at each site and record the average if the tape is being used for a trend. A one-centimetre change in waist or neck can move the estimate even when no meaningful body-composition change occurred. Measurement repeatability is therefore part of the result. Do not compare this circumference estimate directly with a scan, skinfold test, or consumer scale as though each device were measuring the same thing.
Clothing, posture, breathing, and the point at which the tape overlaps can all alter a circumference. Use a flexible tape directly on the body when appropriate and avoid pulling it tight enough to compress tissue. The most defensible comparison is a record made with one method, not a ranking of results from incompatible methods.
It is informational only and is not medical or professional advice.