Formula
Hodgdon and Beckett convert the log of the circumferences into body density, then use the Siri equation. The male form uses waist minus neck. The female form uses waist plus hip minus neck:
Body fat % = 495 / density − 450
Circumferences are stored in centimeters and divided by 2.54 before the published inch formula runs. The result is shown to one decimal place.
Assumptions
- The tape is level and snug, not compressing the skin.
- The female equation adds the hip. The male equation ignores it.
- This is not a DEXA or underwater weighing.
Worked example
A male equation at 178 cm, with a 38 cm neck and an 86 cm waist, estimates 10.8% body fat.
Input definitions
- Waist
- Abdominal circumference at the navel for this method.
- Neck
- Neck circumference below the larynx.
Limitations
This is an informational estimate for adults. It is not a diagnosis, a diet plan, or a training prescription. Pregnancy, illness, and medication can change what is appropriate.
Questions
Why can two people with the same BMI differ?
BMI uses only weight and height. This page uses circumferences, so the result can move when those tapes change.
Does the hip matter for the male equation?
No. The published male formula does not use the hip.