How the Circle Skirt Calculator Works
A circle skirt is cut from a ring of fabric: a small circle in the middle becomes the waist opening and a larger circle around it becomes the hem. Because the waist opening is a circle, its radius follows directly from the circumference formula: waist radius = waist measurement / (2 x pi x fullness), where fullness is 1 for a full circle, 0.75 for a three-quarter circle, 0.5 for a half circle, and 0.25 for a quarter circle. The hem radius is simply the waist radius plus your desired skirt length, and the finished hem circumference is fullness x 2 x pi x hem radius.
Why fullness changes the result
Fullness describes how much of a 360-degree circle the flat pattern uses. A full circle skirt uses the entire ring and gives the most dramatic flare and twirl for a given length. A half or quarter circle skirt covers your waist with a smaller arc, so it needs a proportionally larger radius to reach the same waist measurement — and it produces a narrower, less flared hem. This also means a quarter circle skirt can need a larger pattern span than a full circle skirt of the same length, even though it hangs closer to the body.
How to get the best results
- Measure your waist snugly, over whatever you plan to wear the skirt with, then let the ease input add a little room for comfort.
- Decide your finished length first (waist to hem), not the length of fabric you happen to have.
- Mark the waist and hem radii from the same fixed center point — a string and pencil, or a long ruler pinned at the center, works well for the larger hem curve.
- Add your seam allowance on top of the calculated radii when you actually cut the fabric; the numbers here are finished, sewn measurements.
Reading the fabric numbers
The "fabric diameter" result is twice the hem radius — the minimum span your fabric needs to cover in both directions to cut the panel as one flat piece. Standard quilting cotton runs about 45 inches wide, and apparel or broadcloth fabric often runs 60 inches wide. If your diameter is larger than the fabric you have, plan to cut two half-circle or four quarter-circle panels and sew them together (with seam allowance) to reach the full sweep.