I've been meaning to write this up for a while in my blog, both as a personal note and for anyone who may need the info ~ although 99% of the time I know what I'm knitting with, we all have those brain-fart days where we forget even the most common-knowledge bits of knitting trivia that should be locked in our brains.
Here's a basic guideline of yarn weights and tensions:
1 - super fine - these are also called sock, baby, and fingering yarns. Tension is usually 27–32 sts, using 2.25-3.25mm (US size 1 to 3) needles.
2 - fine - also known as baby or sport weight yarns. Tension is around 23-26 sts, using 3.25-3.75mm (US 3 to 5) needles.
3 - light - a.k.a. DK or Light Worsted weight yarn. Tension is around 21-24 sts, using 3.75-4.5mm (US 5 to 7) needles.
4 - medium - Worsted, Afghan, Aran weight. Tension is generally 16-20sts, with 4.5-5.5mm (US 7 to 9) needles.
5 - bulky - these are Chunky, Craft, and Rug yarns. Tension's approx 12-15 sts, with 5.5-8mm (US 9 to 11) needles
6 - super bulky - better known as Bulky or Roving weight yarns. The tension is 6-11 sts using 8 mm (US 11) or larger knitting needles.
So now we know. :)