Height (inches)

Wrist circumference (inches)

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Wrist ratio examples plotted against the small frame cutoff — 66 / 6.2 = 10.645, just above the 10.4 Small cut-off.

Method & verification

How This Tool Works

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Calculation Method

Computes Body frame from Height and Wrist circumference.

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BoringToolsKit methodology and verification standard

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A worked example: 66 inches, 6.2 inch wrist

Take a person 66 inches tall with a wrist circumference of 6.2 inches. The ratio is 66 divided by 6.2, which equals 10.645. Because 10.645 is above the 10.4 threshold, the frame reads Small. The margin matters: anything between 10.4 and 10.9 sits within about half a point of the boundary, so a wrist measured with a stiff tape, or measured over a wristwatch, can flip the answer. Measuring the wrist just below the wrist bone, with the tape snug but not compressing the skin, keeps the reading within about 0.1 inches, which shifts the ratio by roughly 0.17 for this person.

Contrast that with someone 70 inches tall and a 7.0 inch wrist: 70 divided by 7.0 gives exactly 10.0, solidly Medium. The same 0.1 inch wrist error only moves this ratio by about 0.14. Taller people with proportionally thicker wrists land further from the boundaries, so their classification is more stable. The classification also feeds the healthy-weight range: a small frame typically trims about 10 percent off the midpoint of a standard height-weight table, so a 66 inch person with a Medium-frame range of roughly 118 to 148 pounds would see the upper end drop by about 10 to 15 pounds.

Where the 9.6 and 10.4 cut-offs break down

The ratio method assumes wrist circumference scales linearly with height, but bone structure does not. A 76 inch person with a 7.2 inch wrist scores 10.56 and is classified Small, yet their absolute wrist size is larger than a 60 inch person scoring 9.9 (6.1 inch wrist), who lands Medium. Extremely tall people are systematically pushed toward the Small bucket because the denominator grows faster than skeletal breadth, which is why the classic tables were built mostly from data on people between 60 and 72 inches tall.

Two other edge cases are worth knowing. First, the tape itself: cloth tapes stretch, and measuring over clothing can add 0.2 to 0.5 inches. On a 6.0 inch wrist that inflates the ratio by 0.35 to 0.9, enough to move someone from Small to Medium without any real change in frame. Second, body composition has no effect on the result at all. The ratio reads bone only, so a bodybuilder with a 7.5 inch wrist at 72 inches scores 9.6 exactly, right on the Medium and Large boundary, while their effective carrying weight is far above any standard table. Treat the output as one input to a weight target, not the deciding number.