3.5mm Knitting Needle Size
3.5mm is US size 4 — and worth knowing that neither the UK nor Japanese systems have an exact equivalent for it. Here's what comes closest in each system.
US 4 · UK — no exact match · Japanese ~6号 · Yarn: Sport / Light DK
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Open Needle Size Converter →Enter 3.5mm — or any other size — to see all equivalents side by side.
3.5mm in Every Sizing System
| System | Size | Notes |
|---|---|---|
| Metric | 3.5 mm | The actual diameter |
| US | 4 | |
| UK / Australian | — (no exact) | UK 10 = 3.25mm, UK 9 = 3.75mm — 3.5mm falls in between |
| Japanese | ~6号 | 6号 = 3.6mm — closest available, 0.1mm off |
| Yarn weight | Sport (#2 Fine) | Gauge: approx 24–26 sts per 4" |
About 3.5mm
3.5mm is one of those sizes that exists cleanly in the US and metric systems but leaves a gap in the UK and (almost) in the Japanese scale. The traditional UK wire gauge system jumps from 3.25mm (UK 10) straight to 3.75mm (UK 9), with nothing in between. So if you're working from a British pattern that calls for 3.5mm, it was written using metric sizing rather than a UK number.
Sport weight yarn tends to be underappreciated. It knits up faster than fingering or sock yarn and produces a more lightweight result than DK. Great for three-season garments, lighter children's clothes, and layering pieces.
UK nearest equivalents
If you only have needles labeled in UK sizes and need something close to 3.5mm, your choices are UK 10 (3.25mm) for a slightly tighter result or UK 9 (3.75mm) for a slightly looser one. Swatch both — which one hits your gauge depends on the yarn and your tension.
What to Knit with 3.5mm Needles
Sport-weight socks — not as fine as fingering-weight socks but more durable and a bit quicker to knit. Good for everyday socks that see hard wear.
Children's garments — sport weight in small sizes makes clothing that's lightweight and easy to wash. 3.5mm is a common needle for children's patterns using sport or fine yarn.
Fine accessories — gloves with fingers, detailed mittens, lightweight hats for warmer weather.
Lace on a larger scale — some lace patterns written for sport weight use 3.5mm to get an open-yet-structured fabric. Faster than knitting lace on fingering weight.