Okay, so I've made a bunch of tutus in my life as mother of girls, these I made much the same way except I measured the length from right under their armpits. Jill was 21 inches long. I added an extra 2 inches because as it poofs it raises a bit, plus you need to compensate about an inch for your knot. Kari's ended up being about 32 inches or so.. I used a whole 50 yrd spool of 6 inch tulle plus a little bit for each because I doubled my layers to add volume. Also for the final result they wore their regular tutus under the dresses. Remember that really cool trick to make tutu making easier from this post? Well thanks to Pinterest, I discovered another trick that made making these a breeze!
I should note in here, that for a tutu that goes around the waist I only take about three inches off the elastic, but since I needed it to stay nice and tight on their chests, I took about 5 inches off the measurement. Then I took an extra strip, folded it in half, then looped it through and tied at the back for the shoulder strap. Then do another one. then I took a satin ribbon and just tied it a couple inches down when they were wearing the dresses so that it had a little bit of a shape. And you're done! :)