Yarn Chart

Yarn Weight Conversion Chart and Suggested Needle and Hook Sizes

Yarn Weight Yarn Type (US) Ply (UK, NZ, UA) m/100g Wraps Per Inch (WPI) Suggested Needle Suggested Hook
0 or Lace Thread or Lace 1 to 3 ply 600-800 18+ wpi 2.0-2.25mm (US 0-1) 1.6-1.4mm

(US 6,7,8,B-1)

1 or Superfine Fingering 4 ply 400-480 14 wpi 2.75-3.0mm (US 2) 2.25-3.5mm

(US B-1 to E-4)

2 or Fine Sport 5 ply 300-400 12 wpi 3.25-3.75mm (US 3-5) 3.5-4.5mm

(US E-4 to 7)

3 or Light DK 8 ply 240-300 11 wpi 3.75-4.5mm (US 5-7) 4.5-5.5mm

(US 7 to I-9)

4 or Medium Worsted 10 ply 120-240 9 wpi 4.5-5.5mm (US 7-9) 5.5-6.5mm

(US I-9 to K-10.5)

5 or Bulky Bulky 12 ply 100-130 7 wpi 5.5-8.0mm (US 9-11) 6.5-9mm

(US K-10.5 to M-13)

6 or Super Bulky Super Bulky Less than 100 5-6 wpi 8.0mm+

(US 11+)

9mm+

(US M-13 +)

References:WikipediaYarn Forward
Helpful info:Double two Worsted Strands to make a Bulky.Double two Bulky Strands to make a Super Bulky (especially helpful for those in the UK as I know you have a hard time finding Super Bulky yarns).