Circle Skirt Calculator
Skip the algebra and cut with confidence. Enter your waist measurement, skirt length, seam and hem allowances in inches or centimeters, pick full, three-quarter, half, or quarter circle, and get the waist cutting radius, outer radius, and how much fabric the flat pattern needs.
Example: with Waist circumference 28 · Finished skirt length 22 · Skirt type Full circle · Waist seam allowance 0.5 · Hem allowance 1 → Waist cutting radius: 3.96 in (waist circle, after 0.5 in seam allowance).
- Outer cutting radius26.96 in (radius + 22 in length + 1 in hem)
- Flat pattern / fabric53.9 × 53.9 in flat pattern for a full circle — about 1.50 yd if the fabric is at least 54 in wide; otherwise piece it in halves
Computed by the calculator below using its default values. Change any input to see your own numbers.
Standard drafting: cut radius = waist ÷ (2π × circle fraction) − seam allowance, because sewing the waistband at the seam line enlarges the opening back to your waist. Outer radius adds length and hem.
The geometry of a circle skirt
A circle skirt is a flat donut: the inner circle is your waist, the outer circle is the hem. Since circumference = 2πr, the waist radius is your waist measurement divided by 2π — about 4.5 in for a 28 in waist. For partial circles the waist wraps around only a fraction k of a circle (3/4, 1/2, 1/4), so the radius grows to waist ÷ (2πk): the less circle you use, the bigger the radius and the less flare at the hem.
The seam allowance subtraction trips people up. If you cut the waist opening at exactly waist ÷ 2π and then sew a waistband 0.5 in inside the raw edge, the sewn opening is 0.5 in larger in radius — over 3 in of extra circumference on a full circle. Subtracting the allowance from the cutting radius keeps the finished waist true.
Fitting the pattern on fabric
A full circle's flat pattern spans twice the outer radius in both directions — a 22 in skirt on a 28 in waist needs about a 54 in square, which is why full circle skirts usually demand 60 in wide fabric or piecing from two half circles (add seam allowances on the piecing seams). Half circles need a 2R × R rectangle and quarter circles just R × R. Chiffon and other shifty fabrics reward cutting a full circle on the fold twice; stable cottons can be cut flat.
How it’s calculated
Cut waist radius r = W ÷ (2π × k) − SA, where W is waist circumference, k the circle fraction (1, 0.75, 0.5, 0.25), and SA the waist seam allowance. Outer radius R = r + finished length + hem allowance. Flat pattern bounding box: 2R × 2R for full and three-quarter circles, 2R × R for half, R × R for quarter. Fabric length estimate = pattern length ÷ 36 (yards) or ÷ 100 (meters), valid when fabric width ≥ pattern width. Units pass through unchanged (all-inch or all-cm).
Assumes a non-stretch woven cut flat with no directional print matching — bias-heavy circles also grow at the hem after hanging, so let the skirt hang a day and re-level before hemming.
Cut radius for a 28 in waist (0.5 in seam allowance)
| Skirt type | Circle fraction k | Cut radius |
|---|---|---|
| Full circle | 1 | 3.96 in |
| Three-quarter | 0.75 | 5.44 in |
| Half circle | 0.5 | 8.41 in |
| Quarter circle | 0.25 | 17.33 in |
Computed with r = W/(2πk) − SA; rounded to 0.01 in.
Common mistakes
- Forgetting to subtract the seam allowance from the waist radius — the finished waist ends up 2π × SA too big (over 3 in on a full circle).
- Using the waist radius formula for an elastic-waist skirt, where the opening must instead clear your hips — measure hips and size the opening to slide over them.
- Measuring length from the waist seam but cutting from the raw edge, which shorts the skirt by the seam allowance.
- Hemming immediately: bias sections stretch, so the hem drops unevenly unless the skirt hangs for 24 hours first.
Frequently asked questions
What is the circle skirt radius formula?
Cut radius = waist ÷ (2π × k) − seam allowance, where k is the fraction of a circle (1 for full, 0.75, 0.5, 0.25). A 28 in waist full circle with a 0.5 in allowance cuts at 28 ÷ 6.283 − 0.5 ≈ 3.96 in.
Why subtract the seam allowance from the radius?
Sewing the waist seam moves the effective opening outward by the allowance, enlarging the circumference by 2π × SA — about 3.1 in for a 0.5 in allowance on a full circle. Subtracting it first keeps the finished waist at your measurement.
How much fabric does a full circle skirt take?
The flat pattern is a square with sides twice the outer radius. For a 28 in waist and 22 in length that is about 54 × 54 in, so one skirt takes roughly 1.5 yd of 60 in fabric — or two pieced half circles from narrower goods.
Full, half, or quarter circle — what changes?
Hem sweep and drape. A full circle's hem is 2π × outer radius (very twirly, heavy at the hem), a half circle carries half that flare, and a quarter circle hangs nearly straight. Less circle also means a larger waist radius and less fabric.
Does this work for stretch fabric?
Yes for the geometry, but for a pull-on knit skirt with no zipper the waist opening must stretch over your hips. Size the opening to the smaller of your waist and the hip measurement your fabric's stretch allows, and use a smaller or zero seam allowance.