Knitting Needle & Crochet Hook Size Converter

Why Needle and Hook Sizes Differ Between Countries

The knitting and crochet world never settled on a single global size system. The US uses one set of numbers for knitting needles, the UK/Canada historically used another, and most of Europe and the rest of the world use the metric diameter of the needle in millimeters. To make matters more confusing, the US and UK knitting systems run in opposite directions: a higher US number means a larger needle, while a higher UK number means a smaller needle. The only truly universal measurement is the metric millimeter, which is why most modern patterns list metric sizes as the primary reference and include US or UK equivalents in parentheses.

Reading Patterns From Other Countries

When you pick up a vintage British knitting pattern from a charity shop or download a free pattern from a European designer, do not assume that a needle size labeled "8" matches the "8" stamped on the needles in your craft bag. Always convert to metric first, then find the matching needle in your collection. A US 8 is 5.0 mm; a UK 8 is 4.0 mm. That difference of one full millimeter will change your gauge enough to throw off the fit of any garment.

How Needle Size Affects Your Knitting

Needle size changes the size of the loop you pull through each stitch, which changes how tight or loose the fabric is. Smaller needles make denser, stiffer fabric with more stitches per inch, while larger needles make looser, drapier fabric with fewer stitches per inch. The same yarn can look like a completely different material depending on which size needle you use it with. When a pattern specifies a needle size, it is really specifying the gauge it wants — the size is just the most common way to reach that gauge.

Printable Reference Tables

The two tables above cover every standard knitting needle from 2.0 mm to 20.0 mm and every standard crochet hook from 2.25 mm to 19.0 mm. Save or print the page to keep a handy reference next to your project bag. The converter at the top of the page lets you enter any metric value and snaps to the closest labeled size in the charts, so you can quickly match a pattern's recommendation to whatever is in your needle collection.

Frequently Asked Questions

Is a US size 8 knitting needle the same as UK size 8?

No. A US size 8 is 5.0 mm, while a UK size 8 is 4.0 mm. The UK system counts in the opposite direction from the US system, so always convert by metric millimeters.

How do I convert crochet hook letters to millimeters?

US crochet hooks use letter-number labels like H-8 or J-10. Use the reference table above to map each letter to its metric size — H-8 is 5.0 mm, for example.

What needle size should I use for a worsted weight yarn?

Worsted weight yarn typically works well on 4.5 to 5.5 mm needles (US 7 to 9), with 5.0 mm (US 8) being a common starting size.

Why do some metric sizes have no US equivalent?

The US system does not number every half-millimeter, so sizes like 3.0 mm and 7.0 mm are labeled only in metric and show a dash in the US column.

Are plastic and metal needles the same size?

Yes. Needles with the same metric label have the same diameter regardless of material, though the feel of working with them is different.