Needle & Hook Size Converter
Look up the metric (mm) equivalent for common US and UK/Canadian knitting needle and crochet hook sizes.
Reading the three systems
Metric is the only honest one: it is the shaft diameter in millimetres. US numbers rise with size, UK and Canadian numbers fall, so the two scales cross and there is no formula joining them - the chart is a lookup, not a conversion. A few anchors:
| Metric | US needle | UK needle | US hook |
|---|---|---|---|
| 2.25 mm | US 1 | UK 12 | B-1 |
| 4.0 mm | US 6 | UK 7 | G-6 |
| 5.0 mm | US 8 | UK 5 | H-8 |
| 10.0 mm | US 15 | UK 000 | N/P-15 |
The tables hold 15 needle sizes from 2.0 to 10.0 mm and 14 hook sizes from 2.25 to 10.0 mm. Switch between them with the radio buttons.
Traps in the numbering
- The jump above 6.5 mm. US 10.5 is 6.5 mm and the next listed size, US 11, is 8.0 mm. Nothing labels 7.0 or 7.5 mm, and there are no US 12 or 14 needles.
- Hooks start one size up. The smallest listed hook is 2.25 mm; steel thread hooks below that run on a separate numbering that gets smaller as the number gets larger.
- US hook 7 has no letter. It sits between G-6 and H-8 at 4.5 mm, and the largest three have no UK equivalent, shown as a dash.
Frequently asked questions
What size is a US 8 knitting needle in mm?
5.0 mm, and UK 5 in the old British scale. A US 8 needle and a US H-8 crochet hook are both 5.0 mm, which is coincidence rather than a shared system.
Why do UK needle sizes go down as the needle gets bigger?
They came from wire gauge, where the number counts drawing passes: more passes, thinner wire. So UK 13 is 2.0 mm and UK 000 is 10.0 mm.
How much does one needle size change my gauge?
Usually about half a stitch per inch in stocking stitch. Over a 22 in front that is two inches of width, which is why you reswatch rather than hope.