Knitting needle sizes: US, metric and UK
A knitting needle's size is the diameter of its shaft in millimeters. US needles also carry a number. The chart lists the Craft Yarn Council's standard US size for each, the old UK and Canadian size, the yarn weights whose recommended needle range includes it, and the crochet hook of the same diameter.
Pick any size in the converter above to see it in every system, or step up and down a size when your gauge is off.
| Millimeters | US size | Old UK size | Yarn weight | Same-size crochet hook |
|---|---|---|---|---|
| 1.5 mm | 000 | — | 0 Lace | — |
| 1.75 mm | 00 | — | 0 Lace | — |
| 2 mm | 0 | 14 | 0 Lace | — |
| 2.25 mm | 1 | 13 | 0 Lace, 1 Super Fine | B-1 |
| 2.5 mm | — | — | 1 Super Fine | — |
| 2.75 mm | 2 | 12 | 1 Super Fine | C-2 |
| 3 mm | — | 11 | 1 Super Fine | — |
| 3.25 mm | 3 | 10 | 1 Super Fine, 2 Fine | D-3 |
| 3.5 mm | 4 | — | 2 Fine | E-4 |
| 3.75 mm | 5 | 9 | 2 Fine, 3 Light | F-5 |
| 4 mm | 6 | 8 | 3 Light | G-6 |
| 4.5 mm | 7 | 7 | 3 Light, 4 Medium | US 7 |
| 5 mm | 8 | 6 | 4 Medium | H-8 |
| 5.5 mm | 9 | 5 | 4 Medium, 5 Bulky | I-9 |
| 6 mm | 10 | 4 | 5 Bulky | J-10 |
| 6.5 mm | 10½ | 3 | 5 Bulky | K-10½ |
| 7 mm | — | 2 | 5 Bulky | 7 mm |
| 7.5 mm | — | 1 | 5 Bulky | — |
| 8 mm | 11 | 0 | 5 Bulky, 6 Super Bulky | L-11 |
| 9 mm | 13 | 00 | 6 Super Bulky | M/N-13 |
| 10 mm | 15 | 000 | 6 Super Bulky | N/P-15 |
| 12 mm | — | — | 6 Super Bulky | 12 mm |
| 12.75 mm | 17 | — | 6 Super Bulky, 7 Jumbo | — |
| 15 mm | 19 | — | 7 Jumbo | P/Q |
| 19 mm | 35 | — | 7 Jumbo | S |
| 25 mm | 50 | — | 7 Jumbo | T/U/X |
Where two yarn weights are listed, the size sits where their ranges meet. Some brands label 2.5 mm needles US 1½ and 3 mm needles US 2½, and many sell 12 mm needles as US 17.
Circular needle lengths
The length of a circular needle is measured from tip to tip, including the cable. Choose one a little shorter than the circumference of what you knit in the round, so the stitches reach around without stretching.
| Length | Metric | Usually used for |
|---|---|---|
| 9 in | 23 cm | Socks and baby sleeves in the round |
| 12 in | 30 cm | Sleeves and small hats |
| 16 in | 40 cm | Hats, cowls and neckbands |
| 24 in | 60 cm | Small sweaters, shawls and back-and-forth knitting |
| 32 in | 80 cm | Sweater bodies, shawls and magic loop |
| 40 in | 100 cm | Large sweaters, blankets and magic loop |
| 47 in | 120 cm | Blankets, large shawls and wide projects |
Straight needles usually come in 10-inch (25 cm) lengths for small projects and 14-inch (35 cm) lengths for wider ones. Double-pointed needles come in sets of four or five, about 6 to 8 inches (15 to 20 cm) long.
Choosing a needle size
- Start with the yarn label. Most labels give a recommended needle and a gauge, usually stitches over 4 inches (10 cm) in stockinette.
- Use the pattern's size if it gives one. Pattern designers often knit tighter or looser than the label.
- Knit a swatch. Cast on a few more stitches than the gauge, knit 4 to 5 inches, wash and dry it the way you will treat the finished piece, then count.
- Change needles, not tension. More stitches than the gauge: go up a size. Fewer: go down a size.
The knitting gauge calculator turns your swatch into a cast-on and row count for any size.
Tips
- Trust the millimeters. US labels vary between brands, especially at 2.5, 3 and 12 mm. Most needles have the metric size printed on them.
- Check old needles with a needle gauge. A needle gauge, a card with sized holes, tells you the size of unmarked or vintage needles.
- Material changes gauge. Slick metal needles knit a little faster and often a little looser than wood or bamboo of the same size.
- Ribbing often goes down a size. Many patterns knit cuffs and hems one or two sizes smaller than the body so they pull in.
Frequently asked questions
What size is a US 8 knitting needle in mm?
A US 8 needle is 5 mm, which is old UK size 6. The Craft Yarn Council puts it in the needle range for 4 Medium (worsted) yarn. The sizes either side are US 7 (4.5 mm) and US 9 (5.5 mm).
Is a US 10 knitting needle 10 mm?
No. A US 10 needle is 6 mm. US numbers are size labels, not measurements. A 10 mm needle is a US 15, and a US 10½ is 6.5 mm. When a pattern gives both, go by the millimeters.
What size needles do I need for worsted yarn?
The Craft Yarn Council range for 4 Medium (worsted and aran) yarn is 4.5 to 5.5 mm, US 7 to 9. Many worsted patterns start with US 8 (5 mm). Knit a gauge swatch and go up a size if you have too many stitches per 4 inches, or down a size if you have too few.
How do old UK knitting needle sizes convert to mm?
Old UK and Canadian sizes run backward, so a bigger number is a thinner needle. UK 14 is 2 mm, 13 is 2.25 mm, 12 is 2.75 mm, 11 is 3 mm, 10 is 3.25 mm, 9 is 3.75 mm, 8 is 4 mm, 7 is 4.5 mm, 6 is 5 mm, 5 is 5.5 mm, 4 is 6 mm, 3 is 6.5 mm, 2 is 7 mm, 1 is 7.5 mm, 0 is 8 mm, 00 is 9 mm and 000 is 10 mm.
What length circular needle do I need for a hat?
A 16-inch (40 cm) circular needle suits most adult hats knit in the round. For the crown, as the stitch count drops, switch to double-pointed needles, a 9- or 12-inch circular, or a long 32- to 40-inch circular worked with the magic loop method.
Are knitting needles and crochet hooks sized the same way?
Both are measured in millimeters across the shaft, so a 5 mm needle and a 5 mm (H-8) hook are the same thickness. Their US labels differ, though. US 8 is a 5 mm needle but an H-8 hook, and a US 7 needle and a US 7 hook are both 4.5 mm. Crochet usually takes a larger size than knitting for the same yarn.
Last updated October 20, 2026.