Knitting Needle Size Chart (mm, US, Korea/Japan 호)

Understanding the knitting needle size chart — concept and principle

Knitting needles are labelled in three different systems: metric diameter in millimetres, US numbered sizes, and the Japanese "go" (号) numbers that are also used for straight and circular needles (대바늘) in Korea. A US pattern may ask for US 7 while your needle says 8호. This chart lets you pick a metric size and see the matching US and Japan/Korea numbers, so you can choose the right needle for a pattern or a yarn band.

How it is calculated

There is no formula to type in: the calculator looks up the row of a fixed table for the millimetre size you select and shows the US size and the Japan/Korea number in the same row. A dash means that system has no needle of that exact diameter.

• Japan/Korea 호 (대바늘): 0호 is 2.1 mm and each step adds 0.3 mm, so mm = 2.1 + 0.3 × n for 0호 to 15호 (6.6 mm). Thicker needles are labelled directly in millimetres, such as 7 mm or 8 mm.
• US sizes: an independent numbered scale (US 1 = 2.25 mm, US 4 = 3.5 mm, US 6 = 4.0 mm, US 8 = 5.0 mm, US 10 = 6.0 mm, US 15 = 10.0 mm) with uneven steps.

The principle

What actually controls your fabric is the needle diameter, because the loop of yarn is formed around the needle shaft. Every numbering system is just a label for a diameter. The Japanese system is regular because it uses a fixed 0.3 mm step, while the US steps are uneven. Because the systems step differently, many sizes exist in only one system; 4.5 mm and 6.0 mm are among the few where all three line up.

Worked example

1. Default input: metric size 4.5 mm.
2. The table row for 4.5 mm gives US 7.
3. Japan/Korea check: (4.5 − 2.1) ÷ 0.3 = 8, so the needle is 8호.
4. Result: 4.5 mm = US 7 = 8호.

How to read the result

Use the millimetre value as the reference whenever you can, since it is printed on most needles and yarn bands. If your system shows a dash, take the nearest available size and knit a gauge swatch. More stitches than the pattern per 10 cm means go up a size; fewer means go down.

Common mistakes

• Assuming 8호 means US 8. 8호 is 4.5 mm, while US 8 is 5.0 mm.
• Confusing crochet hook (코바늘) numbers with knitting needle numbers; Japanese crochet hooks use a different scale.
• Relying on old UK sizes, which run in the opposite direction (bigger number, thinner needle).

Frequently asked questions

What is Korean 8호 in mm?

4.5 mm, which is US 7.

What is US 6 in mm?

4.0 mm. It has no exact Japanese number; 7호 is 4.2 mm.

Why does my pattern's gauge not match even with the right needle?

Gauge depends on yarn, tension and needle material as well as diameter. Change the needle size up or down until your swatch matches.

What number are Japanese needles after 15호?

Needles thicker than 6.6 mm are usually labelled in millimetres, such as 7 mm, 8 mm or 10 mm (often called jumbo needles).

Sources: Craft Yarn Council, Standard needle and hook sizes (US/metric)