Yarn Weight Names Around the World

The conversion table

Why ply numbers do not mean plies

This is the confusion underneath the whole table, and it is historical rather than logical.

British and Australian weight names come from a time when yarn was spun from a standard-thickness single, and a 4-ply yarn genuinely had four of those singles twisted together. The thickness of the finished yarn followed from the count.

That is no longer how yarn is made. A modern yarn labeled 4-ply may have two plies, or five, or be a single. The number survives as a weight name and has stopped describing construction. Our yarn ply and twist explained page covers what ply actually means structurally.

Why the equivalences are approximate

It is worth being honest about the limits of a table like the one above.

1. Bands are ranges, not points. Category 4 spans 16 to 20 stitches over four inches. Two yarns at opposite ends of that range are noticeably different.
2. Different traditions divide the range differently. UK DK straddles the boundary between American sport and worsted; there is no single correct mapping.
3. Fiber changes apparent thickness. A lofty woolen-spun wool and a dense mercerized cotton at the same gauge feel like different weights.
4. Manufacturers self-declare. The Craft Yarn Council number is assigned by the yarn company, not by an independent test.

Which is why every page on this site defers to gauge rather than to a name - see gauge and swatching.

How to convert a pattern safely

1. Find the gauge, not the weight name. A pattern that says 20 stitches to 4in on 4.5mm has told you everything.
2. Match your yarn's band gauge to the pattern's. If they agree, the weight names do not matter.
3. If only a weight name is given, use the table above and then swatch. The name gets you to the right shelf; the swatch confirms it.
4. Check the yardage per gram, not just the weight class. Two category 4 yarns can differ by 30 percent in yards per 100g, which changes how many balls you need - see how much yarn do I need.

Other regional differences worth knowing

• Gauge and tension mean the same thing - the first is American usage, the second British.
• Bind off and cast off are the same instruction.
• Needle sizes use different scales, and UK numbering runs backwards relative to US. See the needle size chart.
• Hook sizes are lettered in the US and metric almost everywhere else - see the hook size chart.
• Crochet stitch names differ outright, which is a far more dangerous divergence than yarn weights - see crochet abbreviations US vs UK.

Yardage, which is the number that survives translation

If you are substituting across a weight name you do not recognize, the most robust check is yards per gram.

A yarn with roughly the same yards per 100g as the one the pattern used will behave similarly regardless of what either is called. That is the principle behind yarn substitution, and it is immune to naming conventions entirely.