Sometimes we get patterns from a site in the US and then we need to know how to convert the measures to the ones we use for yarns in Australia and New Zealand.
Here is a yarn conversion chart that might help you.

Conversion tables from US to Metric Needle sizes

USMetric mm
02
12.25
22.75
N/A3
33.25
43.5
53.75
64
74.5
85
95.5
106
10 ½6.5
N/A7
118
139
1510

American Yarn Weight Conversion

AmericaAustralia
Lace Weight1 ply
Baby or fingering2 ply & 3 Ply
Sport weight4 ply
Worsted Weight8 ply double knit
Medium10 ply
Bulky12 to 14 ply