A circle skirt is two radii: a small one that fits the waist and a big one that sets the length. The waist radius comes from dividing by 2π, or less of π for half and three-quarter circles, and everything else is cutting. On knit fabric, enter a waist a little under the real one: the stretch pulls the skirt on without a zipper.
Waist, Length, Fullness
Fullness
Fine-tune: seam allowance and hem
Waist Radius
4.27in
full circle · 30″ waist
Fold the fabric in quarters, arc 4.27″ and 27.27″ from the folded corner, cut both curves.Hang two days before hemming: bias drops.
- Outer radius27.27 in
- Pattern square55 × 55 in
- Fitsone width of 58″ fabric
- Hem to sew168 in
- Fabric, about1 ⅝ yd (pieced halves)
The Formulas
waist radius = waist ÷ (2π × fraction) − seam allowance · outer radius = waist radius + length + hemA half circle wraps the waist around half a circumference, so its radius doubles; a quarter doubles again. The seam-allowance subtraction matters at the waist: cutting the small circle at the raw measurement makes the finished waist bigger by 2π × the allowance, three whole inches at ½ in.
Worked Example
A 30 in waist, 22 in long, full circle, ½ in seams and hem:
- Waist radius: 30 ÷ 6.283 − ½ = 4¼ in. Outer radius: 4.27 + 22 + ½ = 26¾ in.
- The pattern square: 2 × 26.77 ≈ 54 in: exactly a 54 in fabric folded in quarters, or piece two half circles from 45 in fabric (2 yd).
- Hem circumference: about 165 in of narrow hem. Thread the machine and make peace.
Radius Chart, Full Circle
| Waist | Full circle radius* | Half circle radius* |
|---|---|---|
| 24″ | 3.32″ | 7.14″ |
| 26″ | 3.64″ | 7.78″ |
| 28″ | 3.96″ | 8.41″ |
| 30″ | 4.27″ | 9.05″ |
| 32″ | 4.59″ | 9.69″ |
| 36″ | 5.23″ | 10.96″ |
| 40″ | 5.87″ | 12.23″ |
*½ in seam allowance already subtracted.
Cutting and Hanging
- Fold fabric in quarters, pin a tape at the corner, and arc both radii with chalk: a pencil on a string works as well as any tool sold for it.
- Too wide for the fabric? Cut two half circles with seams at the sides, or a ¾ circle with one seam, the calculator flags when the square outgrows common widths.
- Let it hang two days before hemming: bias stretches, and the hem you cut level droops uneven. Re-mark, trim, then hem.
Assumptions and Defaults
- The skirt sits at the measured waist; no ease: circle skirts spin, they don’t squeeze. A zipper or elastic finishes it.
- Elastic-waist versions cut the waist to the hip measurement instead, so it pulls on.
- Fabric check assumes 45 and 58 in widths; pieced layouts add seam allowances at each join.
Circle Skirt Questions, Answered
How do I calculate the circle skirt radius?
The circle skirt waist radius is the waist divided by 2π for a full circle, minus the seam allowance, which gives 4¼ in for a 30 in waist. Half circles divide the waist by π and quarter circles by π/2, so the same waist gives a bigger radius and a straighter hang as the fraction shrinks.
How much fabric do I need for a circle skirt?
A circle skirt needs a square of fabric twice the outer radius on each side, which is 54 in for the example: one length of 54/60 in fabric, or two yards of 45 in fabric pieced as two halves. Longer skirts outgrow a single fabric width quickly, and the calculator flags the point where piecing becomes necessary.
Should I sew a full, half, or three-quarter circle skirt?
A full circle skirt twirls, whereas a half circle drapes more quietly, and a three-quarter circle falls between the two with a single seam. A quarter circle reads as an A-line skirt; all of them use the same math, only with a different fraction of π.
Why does my circle skirt hem dip after a day of wearing?
A circle skirt hem dips because of bias drop: the diagonal sections of the circle stretch under their own weight. Hang the skirt for two days before hemming, re-mark the length from the floor, and the hem will stay level after that.