Why frame size adds context to other measurements
Body frame size — small, medium, or large — reflects skeletal structure rather than fat or muscle mass directly. It's a traditional, informal classification, most often used as context for ideal weight charts: someone with a larger frame naturally carries more bone and lean tissue at a healthy weight than someone with a smaller frame at the identical height.
This calculator uses the classic ratio method: dividing height by wrist circumference, with different thresholds for men and women reflecting average differences in skeletal proportions.
An informal tool, not a clinical one
Unlike more rigorously validated body composition tools elsewhere on this site, frame size classification by wrist ratio is a traditional heuristic rather than a method backed by extensive clinical research. It's best used as light context — for example, explaining why two people of identical height and weight might look noticeably different — rather than as a precise measurement.