A conversion chart comparing metric knitting needle sizes with the Old UK and US numbering systems.
| Metric | UK (old) | USA |
| 2mm | 14 | 0 |
| 2.25mm | 13 | 1 |
| 2.5mm | - | 1.5 |
| 2.75mm | 12 | 2 |
| 3mm | 11 | - |
| 3.25mm | 10 | 3 |
| 3.5mm | - | 4 |
| 3.75mm | 9 | 5 |
| 4mm | 8 | - |
| 4.25mm | - | 6 |
| 4.5mm | 7 | 7 |
| 5mm | 6 | 8 |
| 5.5mm | 5 | 9 |
| 6mm | 4 | 10 |
| 6.5mm | 3 | 10.5 |
| 7mm | 2 | - |
| 7.5mm | 1 | - |
| 8mm | 0 | 11 |
| 9mm | 00 | 13 |
| 10mm | 000 | 15 |
| 12mm | - | 17 |
Approximate sizes only. Use this as a rough guide for determining the size of children's clothing.
| Age | Chest Size (inches) |
| 3 Month | 19-20" |
| 6 Month | 20-21" |
| 12 Month | 21-22" |
| 18 Month | 22-23" |
| 2 Years | 23-24" |
| 3 Years | 24-25" |
| 4 Years | 25-26" |
| 5 Years | 26-27" |
| 6 Years | 27-28" |
| 7 Years | 28-29" |
| 8 Years | 29-30" |
| 10 Years | 30-31" |
| 12 Years | 31-32" |
This guide shows standard UK yarn weights and their US equivalents. Comparisons are not always exact. Needle sizes provide a rough guide only - check the yarn band for a more precise suggestion.
| UK | US | Alternate Names | Suggested Needle Sizes |
| Jumbo | Roving | 12.75mm and larger | |
| Super Chunky | Super Bulky | Roving | 8mm-12mm |
| Chunky | Bulky | Craft, Rug | 5.5mm-8mm |
| Aran | Medium | Worsted | 4.5mm-5.5mm |
| Double Knit | Light | Light Worsted | 4mm-4.5mm |
| Fine | Sport | 3mm-4mm | |
| 4 Ply | Super Fine | Fingering/Sock | 2mm-3mm |
| 3 Ply | Super Fine | Light Fingering/Sock | 2mm-3mm |
| 2 Ply | Lace | 1.5mm-2.5mm |
