Yarn weight guide.

2ply - Essentially two strands of yarn spun together. Great for socks and gloves. Knit on 2 - 3.5mm needles.

4ply - Great for baby clothes, heavier socks and lightweight tops. Knit on 3 - 4mm needles.

DK or double knitting - Essentially double the weight of 4ply. This is the most widely used weight of yarn. Knit on 3.5 - 4.5mm needles.

Aran - Originally created for fisherman's jumpers. Use when DK isn't heavy enough and chunky is too bulky. Knit on 4 - 5.5mm needles.

Chunky - Associated with outdoor wear and winter jumpers. Knit on 5.5 - 7mm needles.

Super Chunky - A great weight for beginners because it produces quick results. Knit on needles that are at least 7mm thick.