Yarn Weight Conversion

Wrap the yarn around a ruler, a dedicated WPI tool, or even a pencil marked at one-inch intervals, keeping each wrap snug against its neighbor without stretching the fiber or leaving gaps. Count every individual wrap that falls within that one inch, then enter that count as WPI. Wrapping too loosely undercounts (making the yarn look heavier/bulkier than it is) and wrapping too tightly overcounts, so a light, even touch with a couple of repeat measurements gives the most reliable category match.

No -- choosing any category other than "Auto-detect from WPI" fully overrides the WPI-based detection. The detected weight, gauge range, and needle sizes all come directly from your manually selected category, and the WPI number you entered plays no role in that calculation. This is useful when you already know the category from a pattern's yardage or gauge listing and just want the matching needle and gauge ranges without winding a WPI sample first.

The gauge range is how many stitches of plain stockinette typically fit into 4 inches (10 cm) at that yarn weight -- a Fingering-weight yarn packs more stitches into that span than a Bulky one. The needle size range is the corresponding starting-point needle diameter in millimeters commonly recommended for that weight. Both figures are pulled directly from the Craft Yarn Council's published Standard Yarn Weight System chart, the industry-standard reference that ball bands and pattern designers use to classify yarn by weight. They answer different questions -- stitch density versus tool size -- and both are starting points you'll confirm with an actual gauge swatch.

Yes -- WPI measures thickness, not fiber behavior, so a wool, a cotton, and a boucle can all measure the same WPI while producing noticeably different fabric. A springy wool at WPI 14 will bloom and fill in more than a flat, inelastic cotton at the same WPI, and a novelty yarn with loft can measure thinner on a ruler than it knits up in practice. Treat the detected category and gauge range as a starting point, then confirm with a swatch in the yarn you're actually using.