I made a zillion tutus when my daughter was little (I was a dance mom). I'm not sure exactly what you're asking, so I'll just tell you how I would make an infant tutu.
First a word of caution: Some of the stiffer tulle fabrics can be very scratchy...even cut (like a paper cut), so use the finer bridal tulle, and if the child is truly an infant, I would fold it double, lengthwise, then encase the gathered raw edges in something soft and flexible (like a lightweight fleece).
To get the fullness you want, you will probably need about 5-6 x her waist in length (before gathering).
So, you start with a piece of tulle, about 12" x 60" (assuming a 10" waist) and 1"x11" strip of soft, stretchy fleece. Fold tulle lengthwise, so it's 6" x 60". Gather the raw edges to about 11", and zig-zag onto the 10 center " of 11" fleece. Trim tulle seam allowance & fold down fleece to encase it. Attach (zig-zag) to a leotard/onesy. TADA :-D
at 10:29 PM on Sep. 29, 2010