Different terminology is used in different countries, and it is often difficult to work out which yarn weight should be used for a non-native pattern. (source: Wikipedia)

USA	UK	Australia	Suggested needle (mm)
Laceweight	1 ply	2 ply	1.5–2.25 mm
Fingering	2 ply	3 ply	2.25– 3 mm
Sock	3 ply	3 ply	2.25— 3.25 mm
Sport	4 ply	5 ply	3.25— 3.75 mm
DK/Light Worsted	DK	8 ply	3.75— 4.5 mm
Worsted	Aran	10 ply	4.5— 5.5 mm
Bulky	Chunky	12 ply	5.5– 8 mm
Super Bulky	Super Chunky	14 ply	8 mm and up