Yarn is classified by its thickness or “weight” (not to be confused with the weight as measured in ounces or grams).
The thickness of the yarn is an important consideration when choosing the right yarn for your project, because it will influence the look, feel, and drape of the finished item. Generally speaking, thicker and heavier yarn will make a more warm, thick and sturdy fabric, while something made with thinner yarn will be more light and lacy.
Yarn Sizes Explained
The Craft Yarn Council has created a system that assigns numbers to each category of yarn thickness, from 0 to 7, with 0 being the thinnest and lightest, and 7 being the thickest. You can usually find the yarn weight and number, along with a suggested hook size, on the label or ball band of the yarn.
- Size 0: Lace weight The thinnest yarn size available. It is frequently used for delicate, lacy items such as shawls, doilies, and fine sweaters. Recommended hook size: 2.25 mm.
- Size 1: Super Fine or Fingering weight Also called sock weight, this yarn is slightly thicker than lace weight and is often used for socks, shawls, and lightweight garments. Recommended hook size: 2.25 to 3.5 mm.
- Size 2: Fine or Sport weight Slightly thicker than fingering weight, it is often used for baby clothes, lightweight sweaters, and accessories. Recommended hook size: 3.5 mm to 4.5 mm.
- Size 3: Light or DK weight Makes for wonderful sweaters, cardigans, and other garments, as well as toys. It can also be referred to as Light Worsted. Recommended hook size: 4.5 mm to 5.5 mm.
- Size 4: Medium or Worsted weight This is a medium weight yarn that is commonly used for blankets, scarves, hats, and other accessories. Recommended hook size: 5.5 mm to 6.5 mm. Size 4 also includes Aran or Heavy Worsted weight, although it is very slightly thicker than Worsted weight. It is often used for warm, cozy sweaters and blankets. Recommended hook size: 6 mm to 8 mm.
- Size 5: Bulky weight This is a thick, heavy yarn that is perfect for warm, cozy blankets, scarves, and hats, as well as home decor. Recommended hook size: 6.5 mm to 9 mm.
- Size 6: Super bulky weight or Roving This yarn is often used for quick, chunky projects such as blankets and scarves. Recommended hook size: 9 mm to 15 mm.
- Size 7: Jumbo weight or Roving The jumbo yarn weight category is the most recent addition to the yarn standards. It is often used to create dramatic accessories or home decor and works up very quickly. It is also a great choice for arm knitting or crocheting. Recommended hook size: 15 mm or larger.
It’s important to note that recommended hook sizes are just a guideline and can vary depending on the project and the tension of the individual crocheter, so always remember to check your gauge!
(It’s also worth noting that there are different categories to describe crochet thread sizes — read more here: A Guide to Crochet Thread Weights.)
Yarn Weights – UK vs US
If you are crocheting outside the US, you may see yarn weight referred to by different terms — such as the “ply”. Ply originated as a way to describe how the yarn was spun. For instance, a 2 ply yarn was made by spinning two strands together. Today, yarn made by modern methods may be any number of strands spun together, without necessarily affecting the thickness of the yarn.
Here are the American Standard Sizes and the equivalent UK/Australian/New Zealand terms:
- Size 1: Sock, Light Fingering, Baby ; 2 or 3 Ply
- Size 2: Sport, Baby ; 4 or 5 Ply
- Size 3: DK, Light Worsted ; 8 Ply
- Size 4: Worsted, Aran ; 10 or 12 Ply
- Size 5: Chunky ; 12 or 16 Ply
- Size 6: Super Chunky, Roving ; 14 or 16 Ply
- Size 7: Ultra ; 16 Ply or more
For further reading:
Standard Yarn Weight System (from The Craft Yarn Council)