How long does my (straight) hair have to be?

to do this curly style? http://www.youtube.com/watch?v=icrUkBaSe...

I am assuming Madonna's hair is either naturally straight or not that curly normally. But, whatever - since my hair is straight, and I want to do it in the small curls and have it be that length when done (an inch or two below shoulders), does it have to be much longer starting out? I will use a small barrel curling iron (I've done it before, but it was long time ago). It is just below my shoulders now so I guess it has a way to go because I want it to be Madonna's length in that video - just like that (when it is done).

How long does my (straight) hair have to be?

Well, I think mid-upper arm to elbow length would be fine.