Here’s a handy table to convert knitting needle sizes across the different sizing systems:
| Metric (mm) | US size | UK size |
|---|---|---|
| 2.00 mm | 0 | 14 |
| 2.25 mm | 1 | 13 |
| 2.50 mm | 1.5 | – |
| 2.75 mm | 2 | 12 |
| 3.00 mm | 2.5 | 11 |
| 3.25 mm | 3 | 10 |
| 3.50 mm | 4 | – |
| 3.75 mm | 5 | 9 |
| 4.00 mm | 6 | 8 |
| 4.50 mm | 7 | 7 |
| 5.00 mm | 8 | 6 |
| 5.50 mm | 9 | 5 |
| 6.00 mm | 10 | 4 |
| 6.50 mm | 10.5 | 3 |
| 7.00 mm | – | 2 |
| 7.50 mm | – | 1 |
| 8.00 mm | 11 | 0 |
| 9.00 mm | 13 | 00 |
| 10.00 mm | 15 | 000 |
| 12-12.75 mm | 17 | – |
| 15-16 mm | 19 | – |
| 19 mm | 35 | – |
| 20 mm | 36 | – |
| 25 mm | 50 | – |
Knitting Pattern Writing Tips from a Tech Editor
Tips for formatting your knitting needle conversions in your patterns:
- Use a consistent format to refer to knitting needle sizes throughout your pattern.
- The most popular format includes both Metric (mm) and US sizes to cater to the vast majority of knitters.
- In your introductory / set-up pages, include a section that lists all knitting needle sizes that will be used. You can also mention which parts of the pattern each needle is used for, such as ribbing.
- If using circular needles, make sure to include the lengths of these as well.
- Make sure to include knitting needle sizes with your gauge / swatch tension.
- To really polish your pattern, watch out for inconsistent spacing! See the examples below.
Knitting Needle Sizing Pattern Writing Examples
A designer’s main priority is ensuring the actual knitting pattern is well written, easy to follow, and free of errors. But to a knitter, the right sized needle is one of the first things they consider, so make sure your knitting pattern doesn’t fall into any of the bad formatting examples.
Good formatting:
You will need:
4.0 mm / US 6 knitting needle
3.5 mm / US 4 knitting needle
The format – order and spacing – is consistent across both needle sizes.
You will need:
US 6 (4mm) knitting needle
US 4 (3.5mm) knitting needle
A different order or different punctuation also works, so long as it is consistent.
You will need:
4 mm (US 6 / UK 8) knitting needle
5 mm (US 8 / UK 6) knitting needle
You can also use all three sizes, but this is less common to see.
Bad formatting:
You will need:
Size 4 knitting needle
Size 5 knitting needle
Is this US sizes? Is this in mm? It’s not clear.
You will need:
4 mm (US 4) knitting needle
3.5 mm (US 3.5) knitting needle
This uses the wrong conversions! Always make sure to check your conversions against a chart like the one above.
You will need:
4mm/US 6 knitting needle
3.5 mm/ US4 Knitting Needle
As a tech editor, while this is technically correct, the inconsistent spacing leaps out at me and doesn’t look at professional.
Which knitting needle size conversion should I use in my pattern?
The metric system (mm) is the most well-known internationally but if you’re looking to make your patterns inclusive, then it depends on the geographic location of your main knitting audience, and you can look at yarns manufactured in those regions to get a better idea.
If you don’t have any yarn from different countries, I am giving you 100% approval to go buy some – if anyone asks, it’s ‘for research purposes’.
Take a look at the ‘ball band’ (it’s still called a ball band even if it’s a skein, cake or ball) and find where it shows the recommended knitting needle sizes. Most yarn bands will include the metric size as default. Yarn manufacturers will use different combinations of knitting needle size conversions: some may include US and metric, others may include UK and metric, and some will use all three.
As a tech editor, I’m used to seeing a combination of US and Metric (mm), which provides enough information for 95% of knitters. My personal preference is to start with the metric sizing, followed by US.
Do British knitters use ‘Metric (mm)’ or ‘UK Size’?
Most UK-based knitters have adapted to the metric system for knitting needle sizes.
Vintage patterns and steel knitting needles from the 1900s would use the ‘UK Size’ format. This was perfect for the materials and yarn production techniques that were available at the time, which were mainly natural fibres.
As synthetic fibres were introduced, and new technological advancements allowed for thicker yarns to be produced, it presented new problems for the traditional UK sizing structure for knitting needles.
From the chart above, you can see that this system becomes an issue when working with larger needles. If a 9mm needle is a UK Size 00, and a 10mm needle equates to UK Size 000, what would a 20mm needle be – a UK Size 0000000000000? (That’s thirteen zeros, if you don’t want to count).
Hence the increase in popularity of the metric system.