Yarn Weight Converter

Yarn weight categories are standardized by the Craft Yarn Council (CYC) to help knitters and crocheters substitute yarns and interpret patterns from different countries. Weight refers to thickness, not mass.

CYC Standard Weight System (0–7 scale):

Wraps Per Inch (WPI), the universal thickness test: Wrap yarn around a ruler for 1 inch without stretching it, count the wraps → WPI

Note that WPI counts run in the opposite direction to the CYC numbers: thin yarn gives a high count because more strands fit in the inch. Sources disagree by a wrap or two at the boundaries, since it depends how tightly you wind, so treat a borderline reading as a boundary rather than a verdict.

The one place they disagree by more than a wrap is lace. This page uses the eight-band Craft Yarn Council scale, where lace is simply “18 or more”. Finer charts split that range into cobweb, lace and light fingering and quote 30 to 40 wraps for the middle of it. Both describe the same yarn; one just cuts the fine end into more bands. If you are wrapping something at 25 wraps per inch, it is lace by this scale and light fingering by the other.

If you work in tex or denier rather than in category names, the yarn weight in tex, denier and WPI page carries those columns and uses this same WPI ladder.

Cross-system equivalents:

Needle/hook size conversion:

• CYC 4 (Medium/Worsted): US 7–9 needles (4.5–5.5mm)
• CYC 5 (Bulky): US 9–11 needles (5.5–8mm)
• CYC 6 (Super Bulky): US 11–17 needles (8–12mm)

Typical length in a 100 g skein

Thickness and length trade off against each other, because a skein is sold by weight. The same 100 g of wool is 875 yards of lace or 66 yards of super bulky, a thirteen-fold spread.

These are the same figures the crochet yarn calculator uses, so a project estimated there converts to grams here and comes out the same. Individual yarns vary by 10 or 15% either way, and the ball band is always right where this table is only typical.

Gauge swatch rule: Always knit a 4"×4" swatch before starting any project. Gauge beats the suggested needle size, so adjust until your stitch count matches the pattern.