Yarn weights
Yarns can vary in thickness, and the same yarn weight can have different names depending on where you are in the world. The chart below provides a general guide to the different names used for the same yarn weight, based on its thickness. However, yarns don't always fit neatly into these categories, and there’s often disagreement about how names align across regions. For example, I’ve seen one website where "Fingering" is listed as roughly equivalent to UK 2ply in one chart, but further down the same page, it’s said that "Fingering" is more like UK 4ply!
That said, the chart offers a helpful reference for understanding where a yarn weight falls on the scale. To ensure your yarn will work for a particular project, it’s always a good idea to knit a gauge swatch.
This list isn’t exhaustive, and there are many more names for yarn weights, both within these regions and across the globe.
The Craft Yarn Council is based in the US.