Frame size explains why two people at the same height can have healthy weights fifteen kilograms apart. Divide your height by your wrist circumference and the classic index sorts small, medium, and large skeletons.
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Scientific references
The skeleton under the statistics
Weight tables in the mid twentieth century listed healthy ranges separately for small, medium, and large frames, acknowledging what mirrors always knew. Bone is dense, about twice the density of muscle, and skeletal mass varies enough between people to shift healthy weight meaningfully at any height. The wrist became the favorite measuring spot because it carries almost no fat or muscle, leaving nearly pure skeleton under the tape.
How the index reads
Divide height in centimeters by wrist circumference in centimeters. Men landing above 10.4 count as small framed, 9.6 to 10.4 as medium, and below 9.6 as large. The female cut points run slightly higher, above 11 small, 10.1 to 11 medium, below 10.1 large. A large framed man and a small framed man of identical height can each be healthy at weights differing by a tenth of their body mass, which is why single number weight targets fail so many people.
Adjusting expectations
The practical use is calibrating ideal weight and FFMI expectations. Large framed individuals sit naturally toward the top of every healthy band and carry muscle more heavily, while small frames sit at the bottom. The elbow breadth method, measuring across the elbow bones with calipers, confirms the wrist result when precision matters, though the wrist alone serves everyday purposes well.
Measure the wrist properly
Wrap the tape snugly around the bony prominence just past the hand, the narrowest point of the wrist, with the hand relaxed and open. Too loose adds phantom centimeters and shifts you a full category. Both wrists are nearly identical in most people, so either one works.