Knitting Needle Size Conversion Chart
Knitting needles are sized in three overlapping systems: US numbers, metric millimetres, and old UK numbers (now obsolete but still found in vintage patterns). The metric millimetre measurement is the only physically meaningful one — it is the actual diameter of the needle. US and old-UK numbers are conventional, and the conversions below are not perfectly linear.
Conversion chart
| Metric | US | Old UK |
|---|---|---|
| 1.5 mm | 000 | — |
| 1.75 mm | 00 | 15 |
| 2.0 mm | 0 | 14 |
| 2.25 mm | 1 | 13 |
| 2.5 mm | — | 12 |
| 2.75 mm | 2 | 12 |
| 3.0 mm | — | 11 |
| 3.25 mm | 3 | 10 |
| 3.5 mm | 4 | — |
| 3.75 mm | 5 | 9 |
| 4.0 mm | 6 | 8 |
| 4.5 mm | 7 | 7 |
| 5.0 mm | 8 | 6 |
| 5.5 mm | 9 | 5 |
| 6.0 mm | 10 | 4 |
| 6.5 mm | 10½ | 3 |
| 7.0 mm | — | 2 |
| 7.5 mm | — | 1 |
| 8.0 mm | 11 | 0 |
| 9.0 mm | 13 | 00 |
| 10.0 mm | 15 | 000 |
| 12.75 mm | 17 | — |
| 15.0 mm | 19 | — |
| 20.0 mm | 36 | — |
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In depth
Always trust the millimetre size when substituting needles between brands or countries. A US 7 from one manufacturer can be 4.5 mm; from another, 4.25 mm. The half-millimetre matters: a single 0.5 mm change in needle size shifts gauge by roughly 5–8% in stockinette.
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Related
Continue exploring with the full needle reference, the yarn weight guides, or the gauge swatch guide.