Knitting Needle Size Converter

Knitting needle sizes use three different systems depending on the country: US numbers, metric millimeters, and old UK/Canadian numbers.

The metric (mm) measurement is the actual diameter of the needle. US and UK sizes are arbitrary numbering systems that map to specific millimeter sizes.

Complete knitting needle size reference table:

Those “none” cells are not gaps in the data, they are gaps in the systems. The three scales were invented independently and never lined up, so 3.5 mm has a US size but no old UK number, while 7.0 mm and 7.5 mm have UK numbers and no US equivalent. The converter above says “no equivalent” in those cases rather than quietly handing you the next size along, which is a real risk: 3.5 mm and 3.25 mm are close enough on paper and different enough in a gauge swatch to change a finished garment by a size.

Key differences between the systems:

• The US system goes from 0 (smallest common) upward, with larger numbers meaning larger needles.
• The old UK system runs in the opposite direction: higher numbers mean smaller needles. UK 14 is very small (2.0 mm) while UK 0 is large (8.0 mm).
• Metric is the most universal and unambiguous system, since it measures the actual needle diameter.

How to choose the right needle size:

• Check your yarn label: it always recommends a needle size range.
• Knit a gauge swatch before starting a project. If your swatch is too tight, go up a needle size. If too loose, go down a size.
• Needle material (wood, metal, bamboo, plastic) also affects tension slightly.

Practical tips:

• When following patterns from different countries, always convert to metric first to avoid confusion.
• A needle gauge tool (a flat card with holes) lets you physically measure any needle whose size markings have worn off.