Metric (mm) to US Knitting Needle Size Conversion
Find the US size for any metric knitting needle — whether you've bought needles labeled in mm or are working from a European pattern.
4.0 mm = US 6 · 4.5 mm = US 7 · 5.0 mm = US 8 · 5.5 mm = US 9 · 6.0 mm = US 10
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Open Needle Size Converter →Enter any mm size and instantly see the US, UK, and Japanese equivalents.
Metric (mm) to US Conversion Chart
Every standard metric needle size with its US equivalent, UK size, and yarn weight. Sizes without a US equivalent are shown with the nearest US size as an approximation.
| Metric (mm) | US Size | UK Size | Japanese | Yarn Weight |
|---|---|---|---|---|
| 1.5 mm | US 000000 | — | — | Lace / Cobweb |
| 1.75 mm | US 00000 | — | — | Lace / Cobweb |
| 2 mm | US 0 | 14 | 0号 | Fingering / Sock |
| 2.1 mm | — | — | 1号 | Fingering / Sock |
| 2.25 mm | US 1 | 13 | ~1号 (approx) | Fingering / Sock |
| 2.4 mm | — | — | 2号 | Fingering / Sock |
| 2.5 mm | US 1.5 | — | — | Fingering / Sock |
| 2.7 mm | — | — | 3号 | Fingering / Sock |
| 2.75 mm | US 2 | 12 | ~3号 (approx) | Sport / DK |
| 3 mm | US 2.5 | 11 | 4号 | Sport / DK |
| 3.25 mm | US 3 | 10 | ~5号 (approx) | Sport / DK |
| 3.3 mm | — | — | 5号 | Sport / DK |
| 3.5 mm | US 4 | — | ~5号 (approx) | DK / Worsted |
| 3.6 mm | — | — | 6号 | DK / Worsted |
| 3.75 mm | US 5 | 9 | ~6号 (approx) | DK / Worsted |
| 3.9 mm | — | — | 7号 | DK / Worsted |
| 4 mm | US 6 | 8 | ~7号 (approx) | DK / Worsted |
| 4.2 mm | — | — | 8号 | DK / Worsted |
| 4.5 mm | US 7 | 7 | ~8号 (approx) | Worsted / Aran |
| 4.5 mm | — | — | 9号 | Worsted / Aran |
| 5 mm | US 8 | 6 | ~9号 (approx) | Worsted / Aran |
| 5.1 mm | — | — | 10号 | Worsted / Aran |
| 5.4 mm | — | — | 11号 | Worsted / Aran |
| 5.5 mm | US 9 | 5 | ~11号 (approx) | Bulky / Chunky |
| 5.7 mm | — | — | 12号 | Bulky / Chunky |
| 6 mm | US 10 | 4 | ~12号 (approx) | Bulky / Chunky |
| 6 mm | — | — | 13号 | Bulky / Chunky |
| 6.3 mm | — | — | 14号 | Bulky / Chunky |
| 6.5 mm | US 10.5 | 3 | — | Bulky / Chunky |
| 6.6 mm | — | — | 15号 | Bulky / Chunky |
| 7 mm | — | 2 | — | Bulky / Chunky |
| 7.5 mm | — | 1 | — | Bulky / Chunky |
| 8 mm | US 11 | 0 | — | Super Bulky / Jumbo |
| 9 mm | US 13 | 00 | — | Super Bulky / Jumbo |
| 10 mm | US 15 | 000 | — | Super Bulky / Jumbo |
| 12 mm | US 17 | — | — | Super Bulky / Jumbo |
| 15 mm | US 19 | — | — | Super Bulky / Jumbo |
| 19 mm | US 35 | — | — | Super Bulky / Jumbo |
| 20 mm | US 36 | — | — | Super Bulky / Jumbo |
| 25 mm | US 50 | — | — | Super Bulky / Jumbo |
Why Your Needle Is Labeled in mm
Metric sizing measures the actual physical diameter of the needle shaft. It is the international standard used across Europe, Scandinavia, Australia, and most of Asia. If you bought needles from a non-American brand — Addi, Lykke, KnitPro, Drops — they are likely labeled primarily in millimeters.
American patterns almost always include both the US size and the mm equivalent (for example, "US 7 / 4.5 mm"), but older American patterns may list only the US number. Use the table above to find the mm size for any US needle you need.
What if the pattern mm size isn't in the table?
Some patterns — especially European ones — call for sizes like 3.9 mm or 4.2 mm that don't have an exact US equivalent. These map to Japanese needle sizes. In practice, the nearest standard US size is used. The most important thing is to knit a gauge swatch and adjust needle size until your stitch count matches the pattern.
Metric is the most reliable measurement
US needle size numbering is an arbitrary scale — a US 6 doesn't physically measure 6 of anything. Millimeters measure the actual needle diameter. If you have needles from different brands or eras and want to be certain of the size, measure the diameter with a needle gauge tool and match the mm value to this chart.
Most Common Metric Sizes and What They're Used For
2.0–2.75 mm (US 0–2): Very fine needles for sock knitting and lace. Requires patience and fine yarn.
3.25–3.75 mm (US 3–5): Sport and DK weight yarn. Good for baby items, lightweight garments, and fine accessories.
4.0–5.0 mm (US 6–8): The most popular range. Works with DK and worsted weight — the yarns used in most published patterns. US 8 (5mm) is the single most commonly purchased needle size.
5.5–6.5 mm (US 9–10.5): Aran and bulky weight. Fast to knit, great for hats, sweaters, and blankets.
8.0 mm and above (US 11+): Super bulky and jumbo yarn. Projects work up quickly and are popular for arm-knitting and beginner projects.