The rule
For knitting in the round, the needle's total length (tip to tip, including the cable) must be shorter than the circumference of the piece, or the stitches will not reach around. For knitting flat, the length hardly matters — longer is simply more comfortable for a wide piece, and a 32" circular is the all-purpose flat needle.
Length by project
| Project | Circumference | Cable length |
|---|---|---|
| Socks, mittens, glove fingers, sleeve cuffs | 6–10" | 9" circular, or double-points, or magic loop on a 32–40" |
| Sleeves, children's hats | 10–16" | 12" or 16" |
| Adult hats, cowls, necklines | 18–24" | 16" |
| Sweater body, child | 24–32" | 24" |
| Sweater body, adult | 32–48" | 24" or 32" |
| Shawls, blankets, wide flat pieces | any (worked flat) | 32", 40" or 47"–60" |
| Blankets in the round, large yokes | 60"+ | 60" |
A hat is the one everyone asks about: a 16" circular for the body, then switch to double-points or magic loop when the crown decreases take the circumference below 16".
Magic loop
With a 40" or longer cable you can knit any circumference, however small, by pulling loops of cable out between two halves of the stitches. One long needle then does socks, sleeves and hats as well as sweaters. It is the reason many knitters own a 40" in every size and nothing shorter. Short circulars (9" and 12") are the alternative for socks and sleeves if the loops annoy you; addi FlexiFlips are a third way — two short bent circulars used like double-points.
Tips
addi Turbo tips are nickel-plated brass: yarn slides over them without catching, which is faster and kinder to the hands once the tension is steady, and slippery for a beginner.
addi Rockets are the same needle with a longer, sharper tip, for lace, cables and any pattern with a lot of decreases and knit-through-back-loop.
addi Rocket2 Squared flattens the shaft to a rounded square, which many knitters with hand pain find easier to hold and which evens out tension.
Bamboo and wood (Crystal Palace, Reynolds rosewood) grip the yarn slightly: slower, warmer, quieter, and the right choice for slippery silk and alpaca, for double-points that must not slide out, and for learning.
Interchangeables
An interchangeable set — addi Clicks — is tips plus a range of cables, and covers most of the table above in one case. The join is the thing to test: it should be smooth enough that a fingering-weight stitch passes without snagging.