Knitting Needle Conversion Chart: US, UK & Metric Sizes
A US 6, a UK 8 and a 4 mm needle are all the same needle. Here's how the three systems line up.
Patterns are written all over the world, and needle sizing never settled on one language. Find your size in any column and read across. If you only remember one thing: trust the millimetres.
| Size | Metric | US | UK (old) | Usually suits |
|---|---|---|---|---|
| 1.5mm | 000 | 17 | Lace, 1–2 ply | |
| 1.75mm | 00 | 15 | Lace, 1–2 ply | |
| 2mm | 0 | 14 | Lace, fine sock | |
| 2.25mm | 1 | 13 | 4 ply, sock | |
| 2.5mm | 1½* | — | 4 ply, sock | |
| 2.75mm | 2 | 12 | 4 ply, sock | |
| 3mm | 2½* | 11 | 4 ply, sock | |
| 3.25mm | 3 | 10 | 4 ply, sock, DK ribbing | |
| 3.5mm | 4 | — | Sport | |
| 3.75mm | 5 | 9 | Sport, light DK | |
| 4mm | 6 | 8 | DK | |
| 4.5mm | 7 | 7 | DK, light aran | |
| 5mm | 8 | 6 | Aran, worsted | |
| 5.5mm | 9 | 5 | Aran, worsted | |
| 6mm | 10 | 4 | Chunky | |
| 6.5mm | 10½ | 3 | Chunky | |
| 7mm | — | 2 | Chunky | |
| 7.5mm | — | 1 | Chunky | |
| 8mm | 11 | 0 | Chunky, super chunky | |
| 9mm | 13 | 00 | Super chunky | |
| 10mm | 15 | 000 | Super chunky | |
| 12mm† | 17 | — | Super chunky | |
| 15mm | 19 | — | Jumbo | |
| 19mm | 35 | — | Jumbo | |
| 25mm | 50 | — | Jumbo, arm knitting |
• The sizes we sell most of — No direct equivalent * Not an official US size; brands label these differently † Sometimes sold as 12.75 mm
The trap in vintage patterns
The old UK numbers run backwards: the bigger the number, the finer the needle. So a UK 8 is 4 mm, while a US 8 is 5 mm. Start a jumper on the wrong one and you're a full millimetre out before you've finished the ribbing.
If a pattern just says "size 8 needles" with no system named, check where it was published. British leaflets from the 1970s and 80s almost always mean the old UK size.
Reading the chart
Millimetres are the only reliable number
US and UK numbers are labels; millimetres are a measurement. Manufacturers can vary by 0.1–0.2 mm from the stated size, which quietly compounds across hundreds of stitches. Where a pattern gives both, follow the mm.
Gaps are normal
The three systems were never designed to map onto each other, so some sizes have no equivalent at all. A 3.5 mm needle has no old UK size; 7 mm and 7.5 mm have no US size. Where you see a dash, go one size either way and swatch.
Always swatch
The needle size in a pattern is the designer's starting point, not a promise. Your tension, the fibre and even the needle material change the result - slick metal tends to loosen your gauge, grippy wood tends to tighten it. Knit a tension square, measure it, and change needle size until it matches. That is what this chart is for.
Not sure what you've got?
If the size has rubbed off an old pair, a needle gauge will tell you in seconds - slide the needle through the holes until you find the one it passes cleanly through. We keep them in the shop, and we're always happy to size up a mystery needle for you at the counter.
Common questions
The ones we're asked most often across the counter on Walcot Street.
What is a 4 mm knitting needle in US and UK sizes?
A 4 mm needle is a US 6 and an old UK 8. It's the size most DK patterns call for, which makes it probably the most-used needle in British knitting.
What is a US 8 knitting needle in mm?
A US 8 is 5 mm, which is an old UK size 6. It's the usual choice for aran and worsted weight yarn.
Are UK and US knitting needle sizes the same?
No - and they run in opposite directions, which is what catches people out. US numbers get bigger as the needle gets thicker: US 0 is 2 mm, US 15 is 10 mm. Old UK numbers do the reverse: UK 14 is 2 mm, UK 000 is 10 mm.
So a UK 8 is 4 mm while a US 8 is 5 mm. Same number, a full millimetre apart.
My pattern just says "size 8 needles" - which size do I need?
Look at where the pattern was published. A British leaflet from the 1970s or 80s almost certainly means the old UK 8, which is 4 mm. An American pattern, or any modern one using US sizing, means US 8 - 5 mm.
If there's nothing to go on, knit a tension square on both and keep whichever matches the gauge the pattern gives.
What size knitting needles should I use for DK yarn?
Most DK patterns are written for 4 mm needles (US 6, UK 8), with 3.75 mm and 4.5 mm used to loosen or firm up the fabric. Ribbing is usually worked a size smaller than the body.
The ball band and the pattern's stated tension always beat a general rule - and so does your own swatch.
What size needles do I need for socks?
Most 4 ply sock patterns use 2.25 mm to 2.75 mm (US 1–2, UK 13–12). That's finer than you'd expect for the yarn, and it's deliberate: a dense fabric wears far longer inside a shoe.
How do I find out what size my knitting needles are?
Use a needle gauge - a flat tool with graded holes. Slide the needle through until you find the smallest hole it passes cleanly through, and read the size off beside it.
Don't try to measure with a ruler. The steps between sizes are as small as 0.25 mm, and no one can read that accurately by eye. Bring a mystery needle into the shop and we'll size it for you.
Can I use a different needle size from the one in the pattern?
Yes - and sometimes you have to. The needle size is the designer's starting point; the number that actually decides whether your jumper fits is the tension.
Knit a square and count the stitches over 10 cm. Too many stitches means your knitting is too tight, so go up a size. Too few means it's too loose, so go down. Keep adjusting until the square matches the pattern.
What size needles should a beginner start with?
4 mm to 5 mm (US 6–8, UK 8–6) with a smooth DK or aran wool. Big enough to see what your hands are doing, small enough to still feel like knitting rather than wrestling.
Wooden or bamboo needles are kinder to start on than slippery metal, because the stitches stay put while you work out what you're doing.
Sizes cross-checked against the Craft Yarn Council needle standard and long-established UK sizing. Stuck on a pattern? Bring it in - we love a puzzle.