I have added a picture help with this technique. It shows a flounce made from doughnut already attached to straight piece of fabric, but not turned over. A leftover piece of doughnut is shown as well.
If you are using a wrinkling fabric, it could be quite laborous to press gathered ruffles. It is much easier to press and looks quite different when the ruffle is made of fabric doughnut or a spiral.
How to make:
Say, you are adding a ruffle to skirt hemline.
1) Doughnut. The shape has two radii: inner and outer. Outer radius = Inner radius Ruffle width. The inner radius will determine how full the ruffle will be  from gengle flounce to tight ripples. Experiment on cheap fabric of similar drape to see the results. To calculate how many doughnuts you will need to cut:
# doughnuts = H/[(IR plus SA)*6.28], where
H is the circumference of skirt hemline,
IR is doughnut inner radius and
SA is seam allowance,
6.28 comes from (2 times Pi) to calculate circumference.
I cut the circles on the fold, usually, to make sure they are symmetrical. That's why I work with radii. You can work with a diameter as well, just remember that diameter equals twice the radius (a very painful mistake on math exam back in school)
2) Spiral: instead of cutting the center out of the circles that you cut out for the doughnuts, you can cut it inside as a spiral. The ruffle fullness will change as you go deeper inside the circle. Good for narrow ruffles for neckline (more ruffle in the front) or armcye.

could you proof this and clarify a bit? Is 'H' the bottom circumference of the skirt? is 2*pi the same as 2 times pi?
9/7/05 7:35 PM
Shouldn't the #donuts = H/{6.28*[IR+SA] } ?
9/8/05 0:32 AM
I should be able to decipher your equation, because I know what you're trying to explain. The 'donut shape' is how I would describe cutting the fabric for a onepiece flounce too. What really throws me is the doubling of pi. To get the circumference when you know the radius of a circle, the equation is: the radius times 2 [or the diameter] times pi [3.1416].
But knowing the measurement of the skirt's hem is the same as knowing the circumference of the inner ring on the donut. This means doing the equation the other way around: Circumference divided by pi equals the diameter of the inner circle of your fabric donut. Then make this circle smaller to add seam allowances.
Ok, I've proofread this 3 times for accuracy...is everyone thoroughly confused now? lol
9/8/05 5:47 AM
Sew Very Tall, I think that Elina is talking about a situation when you don't have enough fabric to make the circumference of the inner circle plus the seam allowance as large as the amount needed at the skirt's hem (or the skirt circumference). She is therefore dividing the skirt's circumference by the circumference of the inner circle plus the seam allowance of the donut to arrive at the number of donuts you would need to cut (and splice together) to equal the circumference of the skirt. Since she only speaks of using the radius of the circle, not the diameter, she does the circumference divided by 2 times pi to arrive at the radius of the inner circle plus seam allowance. Don't you just love fiddling with an equation? It's fun.
9/8/05 8:11 AM
Sew Very Tall and Kathryn, you got it right. The splicing of the doughnut and piecing is not simply because I don't have enough fabric  it's because you need a considerably smaller inner radius for the ruffle circle to achieve the ruffle effect. So, you will have to piece any way you look at it.
9/8/05 10:07 AM
for some reason the '+' in equation does not show. i contacted Depeeka
9/8/05 10:55 AM
If anyone tries either of these techniques, please post a picture. I can understand the math part, but I am still having a problem seeing it.
9/8/05 4:43 PM
This is *so* helpful! Just what I've been looking for. Sometimes I buy patterns just for the sake of the ruffle already calculated to the hem. Thank you!
1/7/07 8:42 AM
I was wondering if anyone can help me with something. I'm making Giselle's Wedding Dress from Disney's Enchanted, and the front of the underskirt has vertical ruffles. Someone suggested that I cut them in a spiral shape instead of gathering them, so I'm going to try it. The skirt will probably be about 40" high, so each spiral will have to be that long. Now, because the equation works for the doughnuts and not the spirals, it ends up being something like 10250 doughnuts or something like that, and there is NO WAY I'm going to cut out more than 10,000 doughnuts. ;) So, does anyone know how I would figure out how many yards of fabric I would need for 20 spirals that are 40" long when extended?
4/24/08 1:08 PM
I can't wait to try this!
7/23/09 10:58 AM