Consider the Lily, the home of designer yarns and patterns.  

Metric	UK	American
2.00 mm	14	0
2.25 mm	13	1
2.75 mm	12	2
3.00 mm	11	-
3.25 mm	10	3
3.50 mm	-	4
3.75 mm	9	5
4.00 mm	8	6
4.25 mm	-	-
4.50 mm	7	7
5.00 mm	6	8
5.25 mm	-	-
5.50 mm	5	9
5.75 mm	-	-
6.00 mm	4	10
6.50 mm	3	10½
7.00 mm	2	-
7.50 mm	1	-
8.00 mm	0	11
9.00 mm	00	13
10.00 mm	000	15

  DIFFERENT YARN WEIGHT TERMS

Weight	Gauge 4'-10 cm	Needles
Fingering Baby 4 Ply	28-32	0-3 US 2-3.25mm
Sportweight 5 Ply	24	3-6 US 3.25-4.25mm
DK 8 Ply	22	4-6 US 3.50-4.25mm
Worsted 10 Ply	20	6-9 US 4.25-5.50mm
Heavy Worsted Aran 12 Ply	16-18	8-10 US 5-6mm
Chunky /Bulky	12-14	10-11 US 6-8mm
Super Chunky/Bulky	8-10	11-15 US 8-10mm

Debbie Bliss Yarns