A circle skirt is one of the most satisfying first garments: no darts, no zipper if you use elastic, and a twirl that makes it worth it. It’s also where many sewists meet geometry for the first time — the waist is a circle, and you need its radius.
The formula
Your waist measurement is the circumference of the waist circle. Circumference = 2 × π × radius, so for a full circle skirt:
Waist radius = waist ÷ (2 × π) — about waist ÷ 6.28
Partial circles use a bigger radius, because the waist only fills part of the circle:
| Skirt | Waist radius | Fullness |
|---|---|---|
| Full circle | waist ÷ 6.28 | Maximum twirl; a full ring of fabric |
| Three-quarter circle | waist ÷ 4.71 | Full, but less fabric than a full circle |
| Half circle | waist ÷ 3.14 | Gentle flare, drapes well |
| Quarter circle | waist ÷ 1.57 | A-line silhouette |
For a 28” waist, a full circle’s waist radius is 28 ÷ 6.28 ≈ 4.46”.
Don’t forget the seam allowance
That radius is the stitching line, where the waistband is sewn on. You cut inside it, so the cutting radius is the stitching radius minus the seam allowance. With a ⅝” seam, 4.46” − 0.625” ≈ 3.83”, so you’d cut the waist at about 3⅞”.
Then the hem: hem radius = stitching radius + skirt length + hem allowance. For a 22” skirt with a ½” hem, that’s 4.46 + 22 + 0.5 ≈ 27”.
Round waist radii to the nearest ⅛” rather than up. Rounding up makes the waist larger — and the skirt slides down.
Elastic waists
A pull-on skirt has to stretch over your hips, so the waist opening is based on the larger of your waist and hip measurements, plus about 2” of ease. A 28” waist and 38” hip gives a 40” opening — then the elastic gathers it back to your waist. Cut the elastic itself shorter than your waist so it holds; the Elastic Length Calculator works out how much shorter for the type of elastic you’re using.
Fabric: the part that surprises people
A full circle with a 27” hem radius is 54” across — wider than most fabric. Depending on that radius and your fabric width, you’ll either fold the fabric to cut two quarters at once, lay out quarters one at a time, or piece the skirt from panels with extra seams. Lightweight fabrics with drape — rayon challis, crepe, lawn — make the most of all that hem.
Skip the arithmetic
The Circle Skirt Calculator takes your waist, length, fullness, seam and hem allowances (and hip, for elastic waists) and gives you every radius plus a fabric estimate and layout for your fabric width.