About this tool
"Frame size" is a rough anthropometric classification — small, medium, or large — meant to describe how much of a person's build is bone and joint structure rather than height or soft tissue. The method below, sometimes attributed to nutrition researcher J. Grant, divides height by wrist circumference (both measured in the same unit) into a single ratio. Wrist alone says little on its own, since taller people naturally have thicker wrists — dividing by height corrects for that. Because men and women have systematically different wrist-to-height proportions, the classification uses separate cutoffs for each sex, and this calculator does the same based on the sex you select above.
This is a decades-old field method designed to need nothing more than a tape measure, not a body-composition scan, and it trades precision for that simplicity. Frame size has historically been used alongside "ideal weight" tables — Devine, Robinson, Miller, and Hamwi, covered in our Ideal Weight Calculator — to nudge a target weight up or down for someone's skeletal build, since those formulas otherwise only look at height and sex. Treat the result here as a loose descriptive label rather than a diagnosis: it says nothing about bone density, health risk, or overall body composition, and re-measuring the same wrist a few millimeters differently can easily shift the outcome by a whole category.
Frequently asked questions
Why does my frame size result differ between men's and women's thresholds?
This tool uses sex-specific thresholds because published skeletal-frame research consistently finds women have proportionally higher height-to-wrist ratios classified as "medium" or "small" compared to men at the same ratio value — in other words, the exact same ratio number can indicate a different relative frame size depending on typical skeletal proportions associated with each sex. Some simplified online versions of this calculator incorrectly apply one universal set of cutoffs to everyone, which would misclassify many people; this tool deliberately uses the sex-specific version found in primary sources.
Does frame size affect my BMI category?
No — this site's BMI Calculator uses the standard WHO thresholds, which apply the same way regardless of frame size (this is actually one of the well-known limitations of BMI, since it can't account for someone's skeletal build). Frame size is more directly useful alongside the older Devine/Robinson/Miller/Hamwi-style "ideal weight" formulas (see our Ideal Weight Calculator), which were historically adjusted up or down based on frame size in some clinical contexts — even though those adjustments were never as rigorously standardized as the base formulas themselves.