Needle & Hook Size Converter 📏
Instant and accurate. No sign-up required. Convert knitting needle and crochet hook sizes between US, UK, and metric (mm) systems. Full reference chart with recommended yarn weight for each size.
How to Use the Needle Size Converter
- To use the converter you only need one known value: a size in any one of the three systems printed on your needle, hook, or pattern. - Patterns from US publishers usually give a US number plus the metric millimetre size in parentheses, UK and older Commonwealth patterns give a UK number, and most modern labels worldwide print the metric diameter, which is simply the shaft thickness in millimetres. - Find your starting value in the chart and read across to the equivalent sizes in the other two systems. - The metric column is the anchor because it measures the physical tool directly rather than relying on a numbered scale that drifts between manufacturers and eras. - The same table covers both knitting needles and crochet hooks, though hooks add their own letter scale (for instance the US H/8 hook is 5.0 mm). - Alongside each size sits a suggested yarn weight band, useful as a sanity check when a vintage pattern lists a needle but no yarn. - Always cross-reference the millimetre value rather than trusting the number alone, especially with second-hand or unlabelled needles you can measure with a needle gauge.
- Conversion is a lookup, not arithmetic, because the systems are not linear, but a few anchor points make the chart easy to read. - In knitting needles, US 0 = 2.0 mm, US 4 = 3.5 mm, US 7 = 4.5 mm, US 8 = 5.0 mm, US 10.5 = 6.5 mm, and US 17 = 12.0 mm. - The UK scale runs in reverse, so a larger needle has a smaller UK number: UK 8 = 4.0 mm while UK 4 = 6.0 mm. - Worked example: a pattern says US 8, but you own only UK-marked needles. - Read US 8 across to 5.0 mm, then 5.0 mm across to UK 6, so a UK 6 needle is the match. - A common trap is assuming the numbers transfer directly: a US 8 (5.0 mm) and a UK 8 (4.0 mm) differ by a full millimetre, which is enough to throw off gauge. - Whenever two charts disagree by a hair, trust the millimetre figure and, if needed, measure the actual shaft with a drilled needle gauge.
- Why does a fraction of a millimetre matter? Gauge is exquisitely sensitive: stepping from 4.0 mm to 5.0 mm can change a sweater's chest by several centimetres over a few hundred stitches, turning a fitted garment into an oversized one. - The converter gets you to the right physical diameter, but the printed size is only a starting suggestion, never a guarantee. - Knitters who run tight or loose routinely go up or down a size to hit the pattern's stated gauge, so always knit and block a swatch before committing. - The recommended yarn-weight column reflects the Craft Yarn Council standard weight system and is a guideline, not a rule; many textured, lace, and drapey effects come precisely from pairing a yarn with a deliberately larger or smaller needle. - Watch out for mislabelled or worn vintage needles, interchangeable tips that have rubbed down, and hooks whose letter and millimetre stamps disagree. - When any doubt remains, set the printed number aside and measure the tool itself, because the millimetre diameter is the one value every system ultimately describes.
FAQ
Which needle size system is most universal?
The metric system (millimeters) is the most universal and precise. US and UK sizes are older systems with some inconsistencies between manufacturers. When in doubt, use the mm size to ensure you have the correct needle.
What needle size should I use for worsted weight yarn?
Worsted weight yarn typically uses US 7–9 (4.5–5.5mm) needles. However, always check the yarn label for the manufacturer's recommendation and swatch to confirm your gauge matches the pattern.
Are US and UK needle sizes the same?
No. US and UK needle sizes use different numbering systems and are not interchangeable. A US size 8 needle is 5mm, while a UK size 8 needle is 4mm. Always verify the mm size when converting between systems.
What is the difference between circular and straight needles?
Straight needles are used for flat knitting (back and forth). Circular needles can be used for both flat and in-the-round knitting. The needle diameter (mm) is the same regardless of needle type — only the length differs.
How do I choose between aluminum, bamboo, and plastic needles?
Aluminum needles are slippery and fast, good for smooth yarns. Bamboo needles have more grip, ideal for slippery yarns like silk or bamboo. Plastic needles are lightweight and flexible. Personal preference plays a big role — try different materials to find what works best for you.