Body composition calculator
Body frame size calculator
Small, medium or large build, from your wrist circumference and height. The term every ideal-weight chart leaves out. Free, instant, no sign-up.
Frame size explains the chart. The coach helps with what you do next.
What is body frame size?
Frame size is a rough description of how much skeleton you carry for your height. It is the missing term in every ideal-weight formula in common use: Devine, Robinson, Miller and Hamwi each give one number per height, while the Metropolitan Life tables they all descend from gave three — one each for a small, medium and large frame. Two people of identical height can differ by several kilograms of bone and joint, and without a frame term a heavy-boned person reads as overweight on a chart that was never built for them.
Why the wrist?
Because there is almost nothing there but bone and tendon. The wrist has no meaningful muscle belly and no fat pad, so the measurement barely moves whether you are trained or untrained, lean or carrying weight. That stability is exactly what a frame measurement needs — it is supposed to describe the part of you that does not change. This page uses the wrist-circumference table published by MedlinePlus, which bands women by height in three rows and gives men a single row.
How to measure your wrist
Wrap a tape around the smallest part of your wrist, just below the wrist bone on the hand side, on your dominant arm. Keep the tape snug against the skin but not tight enough to compress. If you do not have a soft tape, wrap a strip of paper around, mark where it overlaps, and measure the strip against a ruler. The measurement should not change from week to week — if it does, you are measuring in different places.
How much does frame size actually matter?
Less than the old weight tables implied, and more than modern charts admit. The spread between a small and large frame at the same height is on the order of 5 to 7 kg in the Metropolitan tables — real, but nothing like the difference muscle mass makes. Elbow breadth measured with calipers is a slightly better method than the wrist, but it needs the calipers held square across the epicondyles, which is not something anyone does correctly at home with a tape. Treat this as one input to reading a weight chart sensibly, not as a number to optimise.