About this tool
Wraps-Per-Inch Yarn Weight Identifier is a free, in-browser tool for knitters and crocheters trying to name a mystery yarn — a thrift-store cone, a re-wound ball or a stash skein with no band. Wrap the yarn snugly around a ruler for one inch, count the wraps, and the tool tells you the yarn-weight category, the Craft Yarn Council number, a typical stitch gauge and the recommended needle and hook sizes. Everything runs locally; nothing is uploaded.
The method divides your wrap count by the number of inches measured to get wraps per inch (WPI), then reads it against a banded lookup: 18 or more is Lace, 14–17 Fingering, 12–13 Sport, 11 DK, 9–10 Worsted, 7–8 Bulky, 5–6 Super Bulky and fewer than 5 Jumbo. Each band carries its standard needle range in millimeters and US sizes, a matching crochet-hook range and the typical knit gauge over four inches, so a reading of 9 WPI identifies a Worsted-weight yarn.
For the most reliable result, wrap without stretching or crowding the strands and measure over two or three inches, then let the tool divide for you. WPI naturally overlaps a little at the band edges, so treat a borderline reading as a starting point and confirm with a gauge swatch.