US Size 6 (Australian size L approx. 51 mm inside circumference).

US Size 7 (Australian size N, 53mm inside circumference).

US size 8 (Australian size P, 56 mm inside circumference).

A guide:
Size 6 = For Very petite fingers and hands
Size 7 = Medium sized Hand
Size 8 = Medium to Large hands

And depending which finger you want it for!