I am doing this from memory, so hopefully I will get it right…
We will make a pattern for one 1/2 of the circle
1) Get 3.5 yards of 60″ muslin.
2) Find the center on the long side
3) Fold the piece in 1/2 so that you have a square. We will call the “1st Fold”
4) Fold the top edge diagonally down to the “1st Fold” forming a triangle
5) The “1st Fold” forming the left side of the triangle is 60 inches long
6) Use a ruler and permanent marking pen to mark 60″ from the folded point at the top of the triangle to many points across the widest part of the triangle
7) Cut the excess fabric off in an arc connecting the dots
8) Now we need to calculate how much to cut out from the top of the triangle. These instructions assume that you are cutting a skirt for a drop waisted dress. Measure your hips loosely – so if they are actually 39″, the measurement should be around 40″. If you have already cut the bodice of the dress and fitted it (assuming that it has points at the bottom), measure across the bodice at the top of the points and double the number. Now go to a radius calculator, like http://www.datedial.com/datCircle_Solver.asp. Enter the waist size into the “Circumference” field, and click the “Solve others” button. The “Radius” number is the one we’re looking for. Measure from the top of the triangle down to several places below the “radius” distance and mark it with a permanent marker. This means that if the length of the triangle is 60″, and your waist is 40″, then the radius is 6.4″ and the length of the skirt will be 60 – 6.4 = 53.6″ (which is pretty long)
9) Cut in an arc along the dots
When you open the muslin template you will have a perfect 1/2 circle to use as your pattern for cutting the circle skirt. You may wish to have a slightly narrower skirt (as I do), and trim the “sides” to reduce the hem width a bit. This will make more of a cone shape than a full circle.
NOTE: For a dancesport gown I found that a full circle skirt is too full, and just trimming the sides to narrow it didn’t work as well as I would have liked, so I made these modifications.
– Measure the hip circumference (40″ in the example above) and multiple by 3 for 120″. This will now be the circumference of the inner circle.
– The radius of this circle is 19.1. The length of the skirt will now be 60 – 19.1 = 40.9
– Once the pattern is cut, your 1/2 circle pattern will actually be 120/2 = 60. Since we only need 40/2=20, I just folded back the fabric to leave me with that measurement. The only reason for not cutting it is so I can reuse this pattern with different waist/hip measurements.
OK, Call me Cheap... 