Needle & Hook Size Converter

How to use

1. Choose whether you are converting knitting needles or crochet hooks — the two use different size charts.
2. Pick the sizing system your pattern (or your needle/hook) is labelled in: mm, US or UK.
3. Select the size from the dropdown — it is pre-filled with the sizes that exist in that system.
4. Read the result row to find the same size written in mm, US and UK so you can match it against what you have on hand.

Good to know

• Not every size exists in every system — for example UK does not have a standard number for a 3.5mm knitting needle, and this is shown as "no standard equivalent" rather than a guess.
• Gauge is the final word: two needles or hooks stamped with the same mm size can still knit up slightly differently depending on the brand, material (metal, wood, bamboo) and how worn or polished the tip is.
• US crochet hook sizes mix a letter and a number (e.g. H-8) — always match on the number or the mm size, since the letters were assigned inconsistently by different manufacturers over time.

FAQ

Why do knitting needles and crochet hooks have three different sizing systems?

Metric (mm) measures the actual diameter and is consistent worldwide. US and UK/Canadian sizes are older numbering systems from before metrication — US counts up as needles get bigger, while old UK/Canadian sizes count down, which is why they look reversed.

What does the letter in a US crochet hook size like "H-8" mean?

The letter is the traditional US name for that hook and the number is a newer, more consistent index — both refer to the same mm size. Use the mm size to be certain, especially with older hooks or patterns.

What should I do if a size has no standard equivalent in another system?

Use the mm measurement and pick the closest available needle or hook in the system you own — a fraction of a millimetre difference is usually within normal gauge variation and can be adjusted for with a swatch.

My pattern only gives a US size — how do I find the matching mm needle?

Set the system to US, select the size the pattern lists, and read the mm column in the result. That mm figure is what to look for on any needle or hook, regardless of its country of origin.