Standard Yarn Weight System

We've collected the standard and common names of yarn weights and the suggested hook and needle sizes. All the information you need in one diagram:

NUMBER
Standard name	Lace	Super Fine	Fine	Light	Medium	Bulky	Super Bulky	Jumbo
Common name	Lace Thread	Sock Fingering Baby	Sport Baby	DK Light Worsted	Worsted Afghan Aran	Chunky Craft Rug	Roving Super Chunky	Roving
PLY	1-3 ply	4 ply	5 ply	8 ply	10-12 ply	12-14 ply	14-16 ply	16+ ply
Recommended Needle Size Range (mm)	1.5-2.25 mm	2.2-3.25 mm	3.25-3.75 mm	3.75-4.5 mm	4.5-5.5 mm	5.5-8 mm	8-12.75 mm	12.75 + mm
Recommended Needle U.S. Size Range	000-1	1-3	3-5	5-7	7-9	9-11	11-17	17 and larger
Recommended Hook size (mm)	0.5-2.25 mm	2.25-3.5 mm	3.5-4.5 mm	4.5-5.5 mm	5.5-6.5 mm	6.5-9 mm	9-15 mm	15 + mm
Recommended Hook U.S. Size Range	B–1	B–1 to E–4	E–4 to 7	7 to I–9	I–9 to K–10 1⁄2	K–10 1⁄2 to M–13	M–13 to Q	Q and larger

PLY: yarns are composed of two or more single yarns twisted together. Two-ply yarn, for example, is composed of two single strands; three-ply yarn is composed of three single strands.

What shall I do if the yarn manufacturer recommends thicker/thinner hook or needle size?

Sometimes the yarn manufacturer recommends a bit thicker hook or needle size to create more lacy, openwork patterns. It's worth to follow and try the recommended sizes, of course considering your crocheting/knitting style whether it's loose or tight.

What shall I do if the pattern designer recommends thicker/thinner hook or needle size?

The pattern designer sometimes recommends a different hook or needle size to a yarn. It's worth to follow and try the suggested needle size, because it's adjusted to the pattern style (of course considering your crocheting/knitting style whether it's loose or tight). If you are crocheting/knitting a bit looser, then try a bit bigger hook, it's important to choose the right needle size to reach the same pattern size.