Circular needles?

[piperredfern.livejournal.com]

I know that this would be better suited in a knitting community (and it is crossposted to a few different craft communities), but I love the quick response time here so I thought I'd post here as well.

I've decided to invest in circular needles after knitting some legwarmers for a friend on straight needles. I'm thinking size 10 1/2 or 11, but what size (as in inches) should I buy if I'm mainly going to be knitting legwarmers with them?

Thanks!