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Knitting Needle Size Converter
Convert knitting needle sizes between US numbers, metric millimetres and the old UK / Canadian system. Each size shows the yarn weight and typical stitch gauge it is usually paired with, plus the full needle chart.
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I know the
mm
The metric size printed on the needle or a needle gauge
Enter your values to see the result.
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How to use the Knitting Needle Size Converter
- Choose what you know: a US number, a metric size or an old UK size.
- Pick or type the size, for example US 8 or 4.5 mm.
- Press Convert to see all three systems at once.
- Check the yarn weight and typical gauge the needle suits.
- Use the next size up or down if your swatch is too tight or loose.
Needle size by yarn weight
These are the Craft Yarn Council's recommended ranges for the standard yarn weight system. Patterns and yarn labels take priority, and your own tension decides the final size.
| Yarn weight | Also called | Needle (mm) | Needle (US) | Stockinette sts per 4 in |
|---|---|---|---|---|
| 0 Lace | Lace, light fingering, crochet thread | 1.5–2.25 | 000–1 | 33–40 |
| 1 Super Fine | Sock, fingering, baby | 2.25–3.25 | 1–3 | 27–32 |
| 2 Fine | Sport, baby | 3.25–3.75 | 3–5 | 23–26 |
| 3 Light | DK, light worsted | 3.75–4.5 | 5–7 | 21–24 |
| 4 Medium | Worsted, afghan, aran | 4.5–5.5 | 7–9 | 16–20 |
| 5 Bulky | Chunky, craft, rug | 5.5–8 | 9–11 | 12–15 |
| 6 Super Bulky | Super bulky, roving | 8–12.75 | 11–17 | 7–11 |
| 7 Jumbo | Jumbo, roving | 12.75 and up | 17 and up | 6 or fewer |
Getting the size right
- Swatch first. Knit at least a 4 × 4 in (10 × 10 cm) square. Too many stitches per 4 in means go up a needle size; too few means go down.
- Measure unlabeled needles with a needle gauge: the smallest hole the needle slides through is its metric size.
- Material matters. Bamboo and wood grip yarn more than metal, so some knitters go up half a size when switching to wood.
- Circular and double-pointed needles use the same diameter sizes; the cable length is a separate measurement.
- Vintage patterns from the UK, Canada and Australia often quote old sizes such as "No. 10" (3.25 mm) or "No. 8" (4 mm). Convert them before buying needles.
Frequently asked questions
What is US 8 in mm?
A US 8 knitting needle is 5 mm, which is old UK / Canadian size 6. It is the needle most often suggested for worsted (medium, weight 4) yarn.
What US size is a 4 mm knitting needle?
4 mm is US 6 and old UK size 8. It is a common choice for DK (light, weight 3) yarn.
Why do old UK needle numbers go down as needles get bigger?
Old UK and Canadian sizes come from the Standard Wire Gauge, where a higher number means a thinner wire. So UK 14 is a fine 2 mm needle and UK 000 is a 10 mm needle. Today the UK sells needles by metric size.
Which size is the most reliable to go by?
The metric diameter in millimetres. US numbers vary slightly between brands at some sizes (US 17 is sold as 12 mm or 12.75 mm) and some metric sizes such as 3 mm, 7 mm and 7.5 mm have no standard US number.
What needle size should I use for my yarn?
Start with the size on the yarn label. As a guide, the Craft Yarn Council suggests 2.25–3.25 mm for sock/fingering, 3.75–4.5 mm for DK, 4.5–5.5 mm for worsted and 5.5–8 mm for bulky yarn. Then knit a gauge swatch and adjust.
Do crochet hooks use the same sizes?
Both are measured in millimetres, so a 5 mm needle and a 5 mm hook have the same diameter, but the US labels differ: crochet hooks use letters (5 mm is H-8), while knitting needles use numbers (5 mm is US 8).
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.
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