Yarn Weight Converter
Translate yarn weights across the four systems that never agree — US names, UK/AU ply, WPI and CYC category — and get the matching needle and crochet hook sizes.
⚠ Worsted and Aran are both CYC 4; Aran often runs slightly heavier. Swatch to confirm.
Weight ≈ thickness, but it doesn't guarantee gauge — always knit/crochet a swatch before substituting yarn. WPI (wraps per inch) is the most reliable physical measure.
Why yarn-weight names disagree
A US pattern says worsted, a UK/Australian one says 10 ply or aran, and the yarn band might only list WPI. They're describing the same thing from four systems. The Craft Yarn Council (CYC) categories 0–7 line them all up — match the CYC number and you can swap systems safely.
Yarn weight conversion chart (CYC standard)
| CYC | US name | UK/AU ply | WPI | Needle | Hook |
|---|---|---|---|---|---|
| 0 | Lace | 1–2 ply | 30–40+ | 1.5–2.25 mm | steel–2.25 mm |
| 1 | Fingering | 3–4 ply | 14–30 | 2.25–3.25 mm | 2.25–3.5 mm |
| 2 | Sport | 5 ply | 12–18 | 3.25–3.75 mm | 3.5–4.5 mm |
| 3 | DK | 8 ply | 11–15 | 3.75–4.5 mm | 4.5–5.5 mm |
| 4 | Worsted | 10 ply (worsted) / 12 ply (aran) | 9–12 | 4.5–5.5 mm | 5.5–6.5 mm |
| 5 | Chunky | 12–14 ply | 6–9 | 5.5–8 mm | 6.5–9 mm |
| 6 | Super Bulky | 14–16 ply | 5–6 | 8–12.75 mm | 9–15 mm |
| 7 | Jumbo | 16+ ply | 1–4 | 12.75 mm+ | 15 mm+ |
FAQ
No — DK is CYC 3 (8 ply) and worsted is CYC 4 (10 ply), so worsted is one step heavier. They're close and sometimes substituted, but worsted knits up thicker. “Light worsted” sits between them.
Aran is CYC 4 — the same category as worsted, but it usually runs a touch heavier (often labelled 10 ply worsted / 12 ply aran). In US patterns aran is treated as the heavy end of worsted/medium.
Measure WPI: wrap the yarn snugly (not stretched) around a ruler for one inch and count the wraps. More wraps = finer yarn. Then match the WPI to a CYC row above. WPI is the most reliable measure because it's physical, not a naming convention.
No — matching weight is necessary but not sufficient. Always knit or crochet a gauge swatch, and also check yardage and fiber, because two same-weight yarns can still differ in gauge and drape.
Historically ply was the number of strands twisted together, but modern yarns can be thick singles, so ply is now only a rough thickness convention (mostly UK/AU). That's why we map it to ranges, not exact gauges.