To make a half circle skirt, you do need to start with just a teeny bit of math, but don’t worry, it’s easy. You need two measurements: your waist measurement, and a skirt length measurement (the total length you want the skirt to be, from top of waistband to bottom of hem).
Take your waist measurement and divide by 3.14 to get the waist radius. So if your waist is 31 and a half inches, you’ll end up with a waist radius of 10. If you get a weird decimal, just round to the nearest quarter inch.
Then take your length measurement and add it to the waist radius to get the hem radius. I wanted my skirt about 25 inches long, so 10 + 25 = 35.
NOTE: Ok, I have to stop here and add a little more explanation because some people are getting angry at me and telling me I don’t know how to do math 😉 Yes, I am aware that dividing your waist measure by 3.14 gives you the diameter of a circle, not the radius. But that’s ok, because we are making a HALF circle skirt, so the diameter is the measurement we want (you only use the true radius if you are making a FULL circle skirt which requires a lot more fabric)! I am referring to this measurement as a waist radius because you will use that measurement as a radius when you cut out the skirt (see photo below). I promise it works – this is how you make a HALF circle skirt – so please don’t leave me a mean comment about my math ability. Thanks!
You’ll likely need 2 yards of knit fabric, although if the measurements you just got are bigger than mine, you may need a little more than 2 yards. Fold the fabric in half (hamburger, not hot dog) and place it on the ground with the fold going along the top and the selvedge edges running down each side. Measure out from the top corner using the waist radius, moving the yardstick and pinning right at the radius number to create a curve, as shown:
Measure again to create a hem curve, this time using the hem radius number. Cut along the pins…
…then sew down the side seam (make sure fabric is RST at this point).
Next you’ll want to cut 2 waistband pieces from some of the extra fabric. The waistband should be 5 inches tall, and half your waist measurement wide. Make sure the long edges of the waistband pieces go with the stretch in the fabric (side to side as seen below). Place the pieces RST and sew all the way down one short side. On the other short side, sew down a little more than halfway, then leave an opening, and sew the bottom half inch, as shown by dots below.
Fold the waistband in half (right side out) and press. Now you have a skirt piece and a waistband piece, as you see below.
Slide the waistband over the top of the skirt and pin the raw edges together. ***One of the waistband seams has an opening; make sure that opening is facing out at this point.***
NOTE: this skirt will only have one seam, so you can decide if you want it to go down the back, or down one of the sides. When pinning the waistband to the skirt, remember you’ll wants the seams in the waistband to be on each side, so either match up the skirt seam with one of them, or center it in between them.
Sew waistband to skirt, being sure to use a stitch that will stretch. I use my serger here and give the waist a tiny stretch as I sew. If you don’t have a serger, be sure to use a zigzag or stretch stitch here, so the waistband will stretch over your hips when taking it on and off.
Flip the waistband up and press. Cut 2 inch wide elastic to your waist measurement and thread it through the waistband, using a large safety pin. Try on the skirt and figure out how tight you want the elastic, then sew the ends together and trim.
At this point all you have left is to hem the skirt! Make sure to pin and press up the hem before sewing. On knit half circle skirts I fold up only once, and then use a double needle to sew the hem.
NOTE: If your fabric is very stretchy or very heavy, it’s a good idea to hang up the skirt and let it drape for 24 hours before hemming. Since part of the skirt is cut on the bias, it’s possible that some portions will stretch out and hang a little lower than others, which you’ll want to take note of before hemming.