Free & Instant — Needles & Hooks

Needle & Hook Size Converter

Convert knitting needle and crochet hook sizes between US, UK, metric (mm), and Japanese systems — no more pattern confusion.

Enter Your Needle Size

Equivalent Sizes

Complete Needle Size Chart

All standard knitting needle sizes across every system, sorted by diameter.

Metric (mm) US Size UK Size Japanese Yarn Weight
2014—Lace
2.1——0Lace
2.25113—Lace
2.4——1Fingering
2.51.5——Fingering
2.7——2Fingering
2.75212—Fingering
32.5113Fingering
3.25310—Sport
3.3——4Sport
3.54——Sport
3.6——5Sport
3.7559—DK
3.9——6DK
468—DK
4.2——7DK
4.5778Worsted
4.8——9Worsted
586—Worsted
5.1——10Worsted
5.4——11Worsted
5.595—Aran
5.7——12Aran
610413Bulky
6.3——14Bulky
6.510.53—Bulky
6.6——15Bulky
7—2—Bulky
7.5—1—Bulky
8110—Bulky
91300—Super Bulky
1015000—Super Bulky
12.7517——Super Bulky
1519——Jumbo
1935——Jumbo
2550——Jumbo

Frequently Asked Questions

What is the difference between US and UK knitting needle sizes? +
US and UK needle sizes use completely different numbering systems that run in opposite directions. A US size 0 equals a UK size 14 — both are 2 mm needles. As the needle gets larger, US numbers increase while UK numbers decrease. UK sizing stops at 000 (10 mm), while US sizing continues to size 50 (25 mm) for very bulky yarn.
How do I convert mm to a US knitting needle size? +
Enter the mm measurement in the converter above and choose "Metric (mm)" from the dropdown. The converter will show the closest US, UK, and Japanese equivalents instantly. For example, 4.0 mm = US 6, UK 8. Not every mm measurement has a direct US equivalent, so the converter will show the nearest standard size.
Are Japanese knitting needle sizes the same as US or UK sizes? +
No — Japanese needle sizes follow the JIS standard and use a separate numbering system (0–15) with each step increasing by 0.3 mm. Japanese No. 0 starts at 2.1 mm and goes to No. 15 at 6.6 mm. They do not correspond directly to US or UK numbers, though some sizes overlap closely (e.g. Japanese No. 8 = 4.5 mm ≈ US 7, UK 7).
What size is a US 6 knitting needle in metric? +
A US 6 knitting needle is 4.0 mm. This is also equivalent to a UK 8. These are very common all-purpose needles used for worsted weight (aran) yarn.
What is the most common knitting needle size for beginners? +
For beginners, US 7–9 (4.5–5.5 mm / UK 7–5) are the most recommended sizes. They are large enough to see your stitches clearly, work well with worsted weight yarn, and are forgiving of tension inconsistencies. US 8 (5.0 mm) is the single most popular all-purpose needle size.
Do UK and Canadian needle sizes follow the same system? +
Yes — Canada historically used the same needle sizing as the UK. If you have old Canadian patterns that pre-date metrication, the needle numbers will match UK sizes. Most modern Canadian patterns now use metric (mm) sizes.
What is the difference between US and UK crochet hook sizes? +
US crochet hooks use a letter-and-number system (B/1 through S) while UK and Canadian hooks use a descending number system. They share no logical relationship — a US G/6 and a UK 8 are both 4.0 mm, but there's no intuitive connection between those labels. The metric (mm) diameter is the only measurement that means the same thing in both systems.
What size is a US G/6 crochet hook in mm? +
A US G/6 crochet hook is 4.0 mm. This is also equivalent to a UK 8 hook. It's one of the most popular all-purpose hook sizes and typically pairs with worsted or DK weight yarn.
What crochet hook size should a beginner use? +
For beginners, a US H/8 (5.0 mm) or US I/9 (5.5 mm) hook is most recommended. These mid-range sizes work well with worsted weight yarn, which is easy to see and handle. Avoid very small hooks under 3 mm until you're comfortable controlling your tension.
How do I convert UK crochet hook sizes to US sizes? +
UK crochet hook numbers and US letter sizes share no direct relationship — both systems were developed independently. The only reliable bridge is the metric diameter. Enter any UK hook number in the converter above and it will instantly show the US letter size and mm equivalent.

Why needle sizes don't match across countries

The short answer: they were invented in different places, at different times, by people who weren't coordinating with each other.

UK needle sizes come from 19th-century wire gauge standards. British needle manufacturers used the same numbering as steel wire — and wire gauge runs backwards, with higher numbers meaning thinner wire. That's why a UK 14 is the smallest standard needle (2 mm) and UK 000 is one of the largest (10 mm). It made sense in a wire factory. For knitters, less so.

US sizes developed separately and went the other way: size 0 is the smallest, numbers climb as needles get thicker. There's no underlying formula — the gaps between sizes are uneven because the system grew organically over decades rather than being designed from scratch.

Metric (mm) is the only system that tells you anything on its own. A 5 mm needle is 5 mm, everywhere, always. Most patterns written after the 1980s include the mm alongside the US or UK number, and if yours doesn't, that's what this converter is for.

How to use this converter

Pick your system, type the size, hit Convert. If your input has a direct equivalent in the other systems, you'll see it right away. If it doesn't — which is common, especially for metric inputs — the converter shows the nearest standard size and marks it as approximate.

The most reliable way to match needles across systems is always the mm diameter. Two needles labeled differently but sharing the same mm measurement are interchangeable. When in doubt, trust the mm.

If you're working from an old British pattern, the numbers can look alarming at first. Pre-1970s UK patterns sometimes use sizes in the teens that sound huge but are actually fine lace needles — a UK 13 is just 2.25 mm. Run it through the chart and it'll make sense immediately.

Japanese 号 sizes explained

Japanese knitting needles are numbered with 号 (pronounced "go"), which just means "number." The system was standardized under JIS — Japan Industrial Standards — and runs from No. 0 (2.1 mm) to No. 15 (6.6 mm), with each step exactly 0.3 mm apart.

That regularity is the system's biggest advantage. Unlike US or UK numbering where the gaps between sizes vary, 号 increments are perfectly even, which makes it easy to step up or down predictably. The catch is that 号 numbers don't map neatly onto US or UK equivalents — you always have to go through mm to find the match. Japanese No. 8, for example, is 4.5 mm, which happens to match US 7 and UK 7, but that's the math working out, not a designed relationship.

Japanese needles are sold internationally and are well regarded for their precision and smooth finish. If you've picked up a set from a Japanese brand and can't figure out the US equivalent, the converter above will sort it out instantly.

Matching needle size to yarn weight

Patterns always tell you which needle to use, but if you're substituting yarn or knitting without a pattern, needle size and yarn weight need to pair up roughly. Here's a practical starting point:

  • Lace / cobweb — 1.5–2.25 mm (US 000–1)
  • Fingering / sock — 2.25–3.25 mm (US 1–3)
  • Sport / DK — 3.25–4.5 mm (US 3–7)
  • Worsted / aran — 4.5–5.5 mm (US 7–9)
  • Bulky — 6–8 mm (US 10–11)
  • Super bulky — 9 mm and up (US 13+)

Treat these as starting points, not rules. Your personal tension, the yarn's fiber content, and what you're making all affect which needle actually works best. Swatching before you commit is always worth it.

Crochet hook sizing: US letters vs UK numbers

US and UK crochet hook systems developed separately, and they don't translate intuitively. US hooks run from B/1 (2.25 mm) up through S (19 mm) using a letter-and-number label. UK and Canadian hooks use a plain number system that runs in the opposite direction — larger numbers mean smaller hooks, just like the old UK knitting needle system.

The result is that a US G/6 and a UK 8 are the same 4.0 mm hook, but nothing about those labels tells you that. A US H/8 matches a UK 6 (both 5.0 mm). There's no formula. You have to look it up, which is exactly what the chart above is for.

The one thing both systems agree on is the mm diameter, which is why modern patterns almost always include it. If you're working from an older UK pattern that only gives a hook number, check the chart — the mm will settle it immediately.