Converter
Knitting needle sizes
US numbers and millimetres, converted both ways. Above US 8 the numbering stops being reliable, so the millimetre figure is what you should trust.
Needle size chart
Typical yarn weight for each needle size, using the standard gauge ranges.
| Metric | US | Typical yarn weight | Knit gauge |
|---|---|---|---|
| 1.5 mm | 000 | 0 Lace | 33–40 |
| 1.75 mm | 00 | 0 Lace | 33–40 |
| 2 mm | 0 | 0 Lace | 33–40 |
| 2.25 mm | 1 | 0 Lace | 33–40 |
| 2.5 mm | 1.5 | 1 Super fine | 27–32 |
| 2.75 mm | 2 | 1 Super fine | 27–32 |
| 3 mm | 2.5 | 1 Super fine | 27–32 |
| 3.25 mm | 3 | 1 Super fine | 27–32 |
| 3.5 mm | 4 | 2 Fine | 23–26 |
| 3.75 mm | 5 | 2 Fine | 23–26 |
| 4 mm | 6 | 3 Light | 21–24 |
| 4.5 mm | 7 | 3 Light | 21–24 |
| 5 mm | 8 | 4 Medium | 16–20 |
| 5.5 mm | 9 | 4 Medium | 16–20 |
| 6 mm | 10 | 5 Bulky | 12–15 |
| 6.5 mm | 10.5 | 5 Bulky | 12–15 |
| 7 mm | 10.75 | 5 Bulky | 12–15 |
| 8 mm | 11 | 5 Bulky | 12–15 |
| 9 mm | 13 | 6 Super bulky | 7–11 |
| 10 mm | 15 | 6 Super bulky | 7–11 |
| 12.75 mm | 17 | 6 Super bulky | 7–11 |
| 15 mm | 19 | 7 Jumbo | 1–6 |
| 20 mm | 36 | 7 Jumbo | 1–6 |
| 25 mm | 50 | 7 Jumbo | 1–6 |
Why US needle numbers are a trap
The US numbering system was never standardised. US 8 is 5.0 mm in most brands, but some list 5.0 mm as US 9, and above US 11 the numbers diverge completely. Vintage patterns are worse: a 1960s "size 10" can be 3.25 mm, while a modern size 10 is 6.0 mm.
The fix is simple — convert everything to millimetres before you buy or substitute. A needle gauge (the flat plastic card with holes) is the cheapest tool in knitting and settles the question in seconds.
Matching needles to yarn
Lace knits on 1.5–2.25 mm, fingering on 2.25–3.25 mm, sport on 3.25–3.75 mm, DK on 3.75–4.5 mm, worsted on 4.5–5.5 mm, bulky on 5.5–8 mm and super bulky on 8–12.75 mm. Those ranges come from the standard gauge figures, and they assume a typical knitter — your hands may want one size either way.
If you are working from a pattern and your swatch does not match, do not guess: run the numbers through the gauge converter and it will tell you the stitch count and the extra yarn.
Straight, circular or double-pointed — the size does not change
A 4 mm circular needle and a 4 mm straight needle knit the same gauge; only the cord and the tip shape differ. What does change is the fabric you can produce: circulars carry a whole blanket, double-pointed needles close a sock in the round, and straights are for flat pieces. Buy the size you need in the format the project needs, and do not expect a different format to fix a gauge problem.
Tip material matters more than most knitters admit. Metal tips are faster and slippery; wood and bamboo grip, which helps with slick yarns and beginners. Switching from wood to metal at the same millimetre size can move your gauge by a stitch or two over four inches — swatch on the needles you will actually use.
Choosing a needle for the project
- Sweaters and blankets: the size that hits the pattern gauge, in a circular long enough to hold the stitches.
- Socks: usually 2.0–2.5 mm, worked at a tight gauge so the fabric wears well.
- Lace: two to three sizes above the yarn's label, then blocked hard to open the pattern.
- Ribbing: one or two sizes below the body needle, so the edges pull in.
Questions people ask
What size is a 3.25 mm knitting needle in US sizes?
US 3. A 4.0 mm needle is US 6, 4.5 mm is US 7 and 5.0 mm is US 8.
Are size 8 knitting needles the same as 4 mm?
No — US 8 is 5.0 mm. US 6 is 4.0 mm. This is the most common conversion mistake in knitting.
What are the old knitting needle sizes in mm?
The old UK system runs 14 (2.0 mm) down to 000 (10 mm). Most modern patterns use metric, and vintage patterns often need converting.
How do I know what size knitting needle to use?
Start from the yarn's recommended range on the label, then swatch. If your gauge is tighter than the pattern, go up a size; looser, go down.