The chart
Millimeters are the real size — the diameter of the shaft — and the US and UK numbers are names for them. The US scale goes up with the size; the old UK (imperial) scale went down, and it still appears on vintage patterns and older British needles.
| US | mm | Old UK | Yarn it usually knits |
|---|---|---|---|
| 000 | 1.5 | 16 | Lace |
| 00 | 1.75 | 15 | Lace |
| 0 | 2 | 14 | Lace, fine fingering |
| 1 | 2.25 | 13 | Fingering, socks |
| 1.5 | 2.5 | — | Socks |
| 2 | 2.75 | 12 | Fingering |
| 2.5 | 3 | 11 | Fingering |
| 3 | 3.25 | 10 | Fingering, sport |
| 4 | 3.5 | — | Sport |
| 5 | 3.75 | 9 | Sport, DK |
| 6 | 4 | 8 | DK |
| 7 | 4.5 | 7 | DK, worsted |
| 8 | 5 | 6 | Worsted |
| 9 | 5.5 | 5 | Worsted, aran |
| 10 | 6 | 4 | Aran, chunky |
| 10.5 | 6.5 | 3 | Chunky |
| 10.75 | 7 | 2 | Chunky |
| 11 | 8 | 0 | Bulky |
| 13 | 9 | 00 | Bulky |
| 15 | 10 | 000 | Bulky, super bulky |
| 17 | 12 | — | Super bulky |
| 19 | 15 | — | Super bulky |
| 35 | 19 | — | Jumbo |
| 50 | 25 | — | Jumbo |
Two gaps are real: there is no US name for 3.5 mm or 12 mm in the old UK scale, and no UK name for 7.5 mm (UK 1) in the US one. A pattern that asks for a size your needles do not have in that scale is asking for the millimeters.
The stamp wins
Makers round differently at the small end. The chart says a US 1 is 2.25 mm, and that is what Crystal Palace's US 1 is; addi's US 1 is 2.5 mm, and addi also sells plain 2.25 mm and 2.75 mm needles with no US number at all. Across a sock that quarter of a millimeter is a stitch or two an inch. So: read the millimeters off the needle, not the US number, and match the millimeters to the pattern. Every needle on this site is listed by its maker's own label, which is why a size page here may hold a "US 1" and a "2.25mm" side by side.
If a needle has lost its markings, a needle gauge — the flat card with holes — reads it in a second. The hole the needle just passes through is the size.
Which size for which yarn
The yarn column above is where to start, not where to finish. The ball band gives the mill's suggested size and the gauge it got; your pattern gives the gauge it needs; the needle that gets you that gauge is the right one, whatever its number. Knitters who work tightly go up a size, loose knitters go down, and a swatch settles it. The yarn weights guide has the full scale with gauges.
For a project in the round, the needle's length matters as much as its size — the circular needle length guide covers that.
Crochet hooks
Hooks use the same millimeters with a letter on top, and the letters are even less standard than the needle numbers. A US G hook is 4 mm from one maker and 4.5 mm from another; a K is 6.5 mm or 7 mm. Buy by the millimeters, which are stamped on every hook we sell, and treat the letter as a nickname — the crochet hook sizes guide has the full chart. Steel hooks for thread run the other way — a higher number is a smaller hook — and are listed by millimeters too.
What we stock
addi Turbo and Rocket circulars from US 000 to US 19 in 16" to 60" lengths, addi FlexiFlips and Clicks, Crystal Palace bamboo circulars, double-points and straights, Reynolds rosewood, and addi and Crystal Palace hooks. The needle sizes page lists each size with everything we have in it; the addi guide sorts the addi range and the material guide says when bamboo beats metal.