Decision tools built for clarity
Body Fat Calculator
Estimate body-fat percentage from circumference measurements using the documented historical equations.
Choose the unit system and the equation, then enter the height and the neck and waist circumferences (and the hip circumference for the female equation), measured as the guide below describes.
How to measure
The estimate is built from circumferences, so where and how you measure matters as much as the numbers. Measure on bare skin with a flexible, non-stretch tape, standing upright and relaxed with your feet together and your arms at your sides, and read each circumference at the end of a normal breath out.
- Neck
- Just below the larynx (the Adam's apple). Wrap the tape at right angles to the length of the neck, so that it sits slightly lower at the front. Keep the neck relaxed; do not tense or flare it.
- Waist
- Male equation: horizontally round the abdomen at the level of the navel. Female equation: round the narrowest part of the torso, usually between the lowest rib and the navel.
- Hips (female equation only)
- Round the widest point of the buttocks as seen from the side, with the tape level with the floor all the way round.
- Height
- Without shoes, heels together, standing straight and looking ahead, in the unit you selected.
For a reliable estimate: keep the tape snug against the skin without pressing in, and keep it level all the way round. Take each measurement twice and enter the average; if the two readings differ noticeably, measure again.
This historical screening estimate is not a diagnosis or a current military eligibility decision.
Methodology
Formula or transformation
Applies the selected historical circumference equation after normalizing measurements to centimetres.
Variables
- Height normalized to centimetres
- Neck circumference in centimetres
- Waist circumference in centimetres
- Hip circumference in centimetres
- Estimated body-fat percentage
Units
- Centimetre
- Percent
Rounding policy
The estimate is rounded to the declared percentage scale using half away from zero.
The selected male or female circumference equation normalizes measurements to centimetres and produces a deterministic estimate.
Estimate body-fat percentage from circumference measurements using the documented historical equations.
Reviewed sources
- National Academies / NCBI Bookshelf — Body Composition in the Military Services Reviewed on 2026-09-07
- U.S. Department of War — DoW Instruction 1308.03 body composition program Reviewed on 2026-09-07
Formula review history
-
Initial formula, limitations, and source review.
Reviewed 2026-09-07 for formula version hodgdon-beckett-circumference-v1
Assumptions
- Inputs are interpreted using the displayed units and options.
- The calculation follows the methodology and factors listed in the sources.
Limitations
- Display rounding can hide additional decimal places.
- The calculation cannot add accuracy that is absent from the submitted inputs.
- This historical screening estimate is not a diagnosis or a current military eligibility decision.
Worked example
For a 70-inch male with a 15.5-inch neck and 34-inch waist, the estimate is about 16.46%.
Frequently asked questions
Where do I measure the waist and the neck?
Neck just below the larynx; waist horizontally at the navel for the male equation and at the narrowest point of the torso for the female equation; hips (female equation) at their widest point. The measurement guide beside the form shows the positions.
Is this a medical body-composition test?
No. It is a historical circumference estimate used for screening; calipers, scans and clinical assessment measure differently, and the result is not a diagnosis.