Waist to floor
(If this is for over your hoop/farthingale, add on 6-8", or take your waist-floor measurement while wearing the hoop. You can always cut off excess later, so don't be shy.)
The circle petticoat doesn't put as much bulk at the waistline as the square petticoats do. They also look beautiful when dancing.
They require allot more fabric and are a bit trickier to make. They take more time to make than the square petticoats, as well. Because they take more fabric, they are also a bit costlier. I recommend these strictly for over-the-hoop wear.
Lay your fabric out, double thickness, but not folded length-wise as they sell it on the bolts. Fold it width-wise so you get the maximum width. I suggest using 60" wide fabric since it's a bit easier to get a circle skirt out of it. You can do it with 45" if it's not a skirt that will be going over a hoop or farthingale, but it is a bit more difficult to get the length you need.
Find one of the corners that has both a salvage and a folded edge. Measure down six inches from the corner, along the selvage edge, and mark it with a pin. (See diagram below if that's confusing, sometimes things make sense in my head, but not when I write them out. ^^;) Mark the same measurement along the folded edge. Now measure out six inches from the corner, going diagonally across the fabric between the folded and selvage edge, and mark that. Repeat marking out six inches from the corner in 1-2" intervals until you have a small quarter-circle marked out in pins.
Now that you have this marked, go ahead and cut along the curved line. This will be the waistline of your petticoat.
From the waistline, measure out your waist to floor measurement (plus 6-8" if it's over-hoop) in the same manner that you did to find your waistline. Make sure your marks are close enough together that you can find them when you are cutting. I usually have my marks about 3 inches apart.
These measurements should also extend from folded to selvedge edge. Once you have that measured, you may now cut this panel out, following the marks you made.
Once you have all your panels cut out, sew them together along the sides, leaving one seam open 6 inches from the top. This would also be a good time to hem your skirt.
Take your waist measurement and add on 4 inches. The width of your band is personal preference, but remember to make it a bit narrower if this will be a petticoat. I usually go with about a 3" band for a skirt and 1 1/2" band for a petticoat. If you are working on a folded edge, take your waist+4" and divide it in half. The diagram is pretty self explanitory. Don't forget to cut your interfacing with the same measurements. The interfacing and waistband will be treated as one unit from now on.
Gather the waistline of your skirt to fit to your waist measurement, plus 1-1 1/2" for comfort. Leave at least 1 1/2" on either side of the opening ungathered. Pin your waistband to the skirt, leaving room for seam allowence and tab. Try on the skirt. If it is too big, pull in the gather strings a bit. If it is too small, let it out a bit. This is a time for tweaking. It's better to get it right now than have to go back and rip stitches later.
Once you are satisfied with the fit of your skirt, sew the skirt to the waistband. Fold the waistband over and finish the inside by hand. This is also the time to do your tab. Close the band with hooks and bars, and voila!
The last step is to try on your petticoat. Twirl about in it! This pattern also makes a great skirt for a ballgown. You'll see what I mean when you twirl!