Wraps per inch

A way of classifying an unknown yarn by winding it around a ruler for exactly one inch, snugly but without stretching, and counting the strands. Roughly five wraps per inch is bulky, ten is worsted, twelve is DK, sixteen is sport and twenty or more is sock or lace weight.

It is a guide rather than a measurement, because fibre blends and spin density vary. When the yarn matters, weigh a known length instead.