What does the number on a yarn label mean?

It's the Craft Yarn Council weight category, from 0 (lace, the thinnest) to 7 (jumbo, the thickest).

Are wraps per inch exact?

No. WPI depends on how tightly you wrap, and different sources give slightly different ranges. Use it to narrow down the weight, then confirm with a swatch.

Yarn

Yarn Weight Converter

Compare all eight standard yarn weights side by side: names around the world, recommended hooks, typical gauge, approximate wraps per inch, yardage and best uses.

Yarn Weight & International Ply Converter

Craft Yarn Council (CYC) standards 0 to 7 with UK/AUS ply equivalents & WPI

Select a Standard Yarn Weight Category (0 to 7):

CYC Category #4

Medium

Common Aliases:

Worsted · Afghan · Aran

UK & AUS Equivalent10-ply / Aran

Traditional terminology

Wraps Per Inch (WPI)9-12 WPI

Fibers wrapped side-by-side

Recommended Hook5.50 – 6.50 mm

US size: I-9 to K-10.5

Typical Yardage / 100g180–220 yds (165–200 m)

Average standard skein length

Typical Single Crochet Gauge (4 inches):11–14 sts

Best Project Applications:Most popular all-around: afghans, beanies, mittens, home decor, scarves

Multi-Strand Substitution Secret: If you don't have bulky yarn, hold lighter yarns together! Two strands of #1 Fingering = #3 DK. Two strands of #3 DK = #5 Bulky. Two strands of #4 Worsted = #6 Super Bulky.

Twisted skeins of teal, grey and copper yarn

How to use the yarn weight converter

Row 1Select a yarn weight category, from #0 lace to #7 jumbo.
Row 2Read its common names, including UK and Australian ply names, and its recommended hook sizes.
Row 3Check the typical crochet gauge and approximate yardage per 100 g to compare yarns.
Row 4Use the wraps-per-inch range to identify yarn without a label.

Based on the Craft Yarn Council standard

The weight numbers, yarn names, hook ranges and gauges come from the Craft Yarn Council's Standard Yarn Weight System, the 0–7 scale printed on most US yarn labels. The CYC presents these as guidelines, the most common hooks and gauges for each weight, so your pattern's gauge always takes priority.

A few columns are approximate rather than official: the UK and Australian ply names, the wraps-per-inch ranges, and the yards per 100 g. These vary between yarns and sources, so use them to compare and narrow things down, not as exact specifications.

Using it to substitute yarn

Swapping one yarn for another works best when you:

1.Stay in the same weight category, for example #4 for #4.
2.Match the pattern's gauge with a swatch, adjusting your hook if needed.
3.Buy by total length. Multiply the pattern's skeins by their yards per skein, then divide by your new yarn's yards per skein. The skein calculator does this for you.
4.Think about fiber. Cotton is heavier and less springy than wool, and acrylic is light and easy to wash, so the same pattern can feel quite different.

For a deeper dive, read our complete yarn weight guide.

Identifying yarn without a label

Wrap the yarn snugly around a ruler, with strands side by side and not overlapping, and count how many wraps fit in one inch. Compare that number with the WPI ranges in the converter to find the likely category, then make a small swatch with the recommended hook to confirm. Ranges overlap because wrapping tension varies, so treat WPI as a strong hint rather than proof.

Tips

DK (#3) and worsted (#4) are different categories. DK is thinner, so check gauge before substituting.
Aran sits at the thicker end of the medium category and is often a little heavier than worsted.
"8-ply" in Australia and New Zealand is roughly equivalent to DK.
For amigurumi, go a hook size or two smaller than the recommended range for a tight fabric.