Needle Size Converter
UK sizes run inversely — higher numbers = thinner needles (UK 14 = 2mm, UK 000 = 10mm).
Japanese numbered sizes (0–15) apply up to 6.6mm; larger Japanese needles use metric directly.
Note: Actual diameters may vary slightly by manufacturer. Always check with a needle gauge.
Select a Needle Size
Choose your input system (mm, US, UK, or Japanese), enter or select a size, and instantly see the equivalents in all other systems plus yarn weight recommendations.
Complete Needle Size Reference Chart
| mm | US | UK | Japanese | Yarn Weight |
|---|---|---|---|---|
| 1.5 | 000 | 15 | — | #0 Lace |
| 2 | 0 | 14 | 0 | #0 Lace |
| 2.25 | 1 | 13 | 0/1 | #1 Super Fine |
| 2.4 | — | — | 1 | #1 Super Fine |
| 2.5 | 1.5 | 12-13 | 1 | #1 Super Fine |
| 2.7 | — | — | 2 | #1 Super Fine |
| 2.75 | 2 | 12 | — | #1 Super Fine |
| 3 | — | 11 | 3 | #1 Super Fine |
| 3.25 | 3 | 10 | — | #1 Super Fine |
| 3.3 | — | — | 4 | #1 Super Fine |
| 3.5 | 4 | — | — | #2 Fine |
| 3.6 | — | — | 5 | #2 Fine |
| 3.75 | 5 | 9 | — | #2 Fine |
| 3.9 | — | — | 6 | #2 Fine |
| 4 | 6 | 8 | 6 | #2 Fine |
| 4.2 | — | — | 7 | #3 Light |
| 4.5 | 7 | 7 | 8 | #3 Light |
| 4.8 | — | — | 9 | #3 Light |
| 5 | 8 | 6 | 10 | #3 Light |
| 5.1 | — | — | 10 | #3 Light |
| 5.4 | — | — | 11 | #4 Medium / Worsted |
| 5.5 | 9 | 5 | — | #4 Medium / Worsted |
| 5.7 | — | — | 12 | #4 Medium / Worsted |
| 6 | 10 | 4 | 13 | #4 Medium / Worsted |
| 6.3 | — | — | 14 | #4 Medium / Worsted |
| 6.5 | 10.5 | 3 | — | #4 Medium / Worsted |
| 6.6 | — | — | 15 | #5 Bulky |
| 7 | — | 2 | uses mm | #5 Bulky |
| 7.5 | — | 1 | uses mm | #5 Bulky |
| 8 | 11 | 0 | uses mm | #5 Bulky |
| 9 | 13 | 00 | uses mm | #6 Super Bulky |
| 10 | 15 | 000 | uses mm | #6 Super Bulky |
| 12 | 17 | — | uses mm | #6 Super Bulky |
| 16 | 19 | — | uses mm | #7 Jumbo |
| 19 | 35 | — | uses mm | #7 Jumbo |
| 25 | 50 | — | uses mm | #7 Jumbo |
| 30 | 65 | — | uses mm | #7 Jumbo |
| 35 | 85 | — | uses mm | #7 Jumbo |
How to Use the Needle Size Converter
Choose Tool Type and Lookup Mode
Select 'Knitting Needle' or 'Crochet Hook' at the top of the form. Then choose 'Convert by Size' to look up a specific needle size, or 'Find by Yarn Weight' to see which needle sizes are recommended for a particular yarn weight category.
Select Your Input System
If converting by size, choose the system your pattern uses: Metric (mm) for modern international patterns, US for American patterns, UK for vintage British or Canadian patterns, or Japanese for Japanese craft patterns. The input field will update to show either a number entry box (for mm) or a dropdown of standard sizes.
Enter or Select the Needle Size
Type in the mm value or choose from the dropdown. All equivalent sizes in every other system appear instantly. If your mm value falls between standard sizes, the converter shows the two nearest sizes and notes that no exact standard equivalent exists.
Use the Reference Table and Export
Scroll down to the full reference table to browse all standard sizes. Use the search box to filter by any value. Click 'Export CSV' to download the full chart as a spreadsheet, or 'Print Chart' to print a clean paper reference copy for your knitting bag.
Frequently Asked Questions
Why do UK needle sizes go down as the needle gets bigger?
The UK sizing system is based on historical British metal wire gauge standards from the industrial era. In that system, higher gauge numbers indicated thinner wire (and therefore thinner needles). The system runs inversely: UK size 14 equals 2mm while UK size 000 equals 10mm. This is the opposite of the US system where larger numbers generally mean larger needles. The old UK system was the standard in Britain and Canada until the 1970s–1980s when metric sizing took over. Today it appears almost exclusively in vintage patterns, so the ability to convert these sizes is essential for crafters working from older books and magazines.
What does it mean when the Japanese size says 'uses mm'?
The Japanese numbered knitting needle system (sizes 0–15) only covers needles up to 6.6mm diameter. Above that threshold, Japanese patterns and needle manufacturers switch to stating the millimeter diameter directly rather than using a special Japanese size number. So a Japanese pattern calling for needles larger than 6.6mm will simply write the mm value (for example, 8mm or 10mm) without a Japanese size number. When our converter shows 'uses mm' for Japanese size, it means the needle in question is above the 6.6mm boundary and no Japanese number designation applies — just use the metric size.
Why do some metric sizes have no US equivalent?
The US needle sizing system was not designed to align perfectly with metric millimeters — it evolved independently from American manufacturing conventions. As a result, there are gaps where common metric sizes have no corresponding US number. For example, 3.0mm falls between US 2 (2.75mm) and US 3 (3.25mm) with no US 2.5 designation. Similarly, 7.0mm and 7.5mm both fall between US 10.5 (6.5mm) and US 11 (8mm). The converter displays a dash (—) for these gaps. In practice, when a pattern specifies one of these metric sizes, simply use the nearest US size and verify gauge with a swatch.
Do the same size numbers apply to straight, circular, and DPN needles?
Yes — the size designation refers to the diameter of the needle tip, which is identical across all needle types. US size 7 (4.5mm) means 4.5mm diameter whether you are using straight single-pointed needles, double-pointed needles (DPNs) for small-circumference projects like socks, circular needles for seamless garments, or interchangeable tips that screw onto different cable lengths. The only needle type that does not follow this system is the cable needle (used solely for holding stitches in cable patterns) — those are typically sized to complement the working needles rather than following the standard size chart.
How do I use this converter to match a yarn weight to the right needle?
Switch to 'Find by Yarn Weight' mode using the toggle at the top of the converter. Then select your yarn weight category from the dropdown — options run from #0 Lace (cobweb and thread) through #7 Jumbo (extreme arm knitting). The tool will display all the needle sizes recommended for that yarn weight in every system. These ranges follow the Craft Yarn Council (CYC) standard, which is printed on most commercial yarn labels. Always make a gauge swatch at the recommended size and adjust up or down as needed to match the pattern's stitch gauge.
What if my needle has no markings — how do I find its size?
For unlabeled needles, use a physical needle gauge — a flat card or metal plate with holes of standard sizes punched into it. Slide the needle into each hole until you find the smallest one it passes through cleanly; that hole size is your needle's diameter in mm. Many needle manufacturers sell needle gauges, and they are inexpensive at craft stores. Once you have the mm measurement, enter it into this converter's Metric (mm) input to find the US, UK, and Japanese equivalents. Note that if your gauge tool reads in US or UK sizes, those may have slightly different mm values depending on the gauge's age — metric is always the most reliable reference.