Circle Skirt Calculator
Waist radius, cutting radii, fabric yardage and a labeled pattern diagram for full, three-quarter, half and quarter circle skirts — in inches or centimeters.
Your measurements
Your pattern
Pattern diagram
Diagram is schematic (not to scale for cutting). Mark both arcs from the same center point.
Fabric needed by width
| Fabric width | Raw need | Buy (rounded up) |
|---|
Conservative bounding-box packing on plain fabric (pieces may be rotated). Muslin-test expensive fabric.
Quick reference: waist radius by size
Length 22 in, ease 0, allowances 5/8 in + 1 in. r = waist / (2 x pi x f).
| Waist (in) | r full (in) | r half (in) | Outer cut, full (in) | Square side, full (in) | Hem, full (in) |
|---|---|---|---|---|---|
| 26 | 4.14 | 8.28 | 27.14 | 54.28 | 164.23 |
| 28 | 4.46 | 8.91 | 27.46 | 54.91 | 166.23 |
| 30 | 4.77 | 9.55 | 27.77 | 55.55 | 168.23 |
| 32 | 5.09 | 10.19 | 28.09 | 56.19 | 170.23 |
| 34 | 5.41 | 10.82 | 28.41 | 56.82 | 172.23 |
Worked examples
Full circle, inches
- Waist 28 in, ease 0, length 20 in, allowances 5/8 in + 1 in, 60 in fabric.
- Waist radius r = 28 / (2 x pi) = 4.46 in.
- Waist cut = 4.46 - 0.625 = 3.83 in; outer cut = 4.46 + 20 + 1 = 25.46 in.
- Square side = 50.91 in -> buy 1.50 yd. Hem = 153.66 in.
Quarter circle, inches
- Waist 28 in, length 20 in, same allowances, 60 in fabric.
- Waist radius r = (2 x 28) / pi = 17.83 in (4x the full-circle radius).
- Outer cut = 38.83 in; square side = 77.65 in; buy 4.38 yd.
Full circle, metric
- Waist 75 cm, length 60 cm, allowances 1.5 cm + 2.5 cm, 150 cm fabric.
- Waist radius r = 75 / (2 x pi) = 11.94 cm; outer cut = 74.44 cm.
- Square side = 148.87 cm -> buy 150.00 cm.
How it calculates
Waist cut radius = r − waist seam allowance. Outer cut radius = r + finished length + hem allowance. Finished hem arc = sector angle × (r + length). Fabric is estimated by packing each panel's bounding rectangle onto the fabric width (greedy first-fit rows, rotation allowed for plain fabric), then rounding up — to the next 1/8 yd, or the next 5 cm in metric.
Assumptions, stated plainly: (1) the skirt is an annular sector and the waist arc equals waist + ease — the convention used by major sewing references; (2) allowances sit outside the seamlines; (3) plain fabric, conservative estimate; (4) stretch fabrics need less ease. This tool drafts skirt bodies and waistbands; it does not draft knit/crochet garments or upholstery covers.
Frequently asked questions
What is the waist radius formula for a circle skirt?
A circle skirt is an annular sector: the waist is the inner arc, so arc length = radius x angle. With waist W (body waist + ease) and skirt fraction f, the waist seamline radius is r = W / (2 x pi x f). That gives: full circle r = W / (2 x pi); three-quarter r = W / (1.5 x pi); half circle r = W / pi; quarter circle r = (2 x W) / pi. Example: a 28 in waist full circle skirt has r = 28 / (2 x pi) = 4.46 in. The same waist as a quarter circle needs r = (2 x 28) / pi = 17.83 in - four times larger, because a shorter arc must still wrap the whole waist.
How much fabric do I need for a circle skirt?
You need a square of fabric whose side equals twice the outer cut radius (waist radius + skirt length + hem allowance). Example: 28 in waist, 20 in long full circle skirt with 5/8 in waist and 1 in hem allowances: waist radius 4.46 in, outer cut radius 25.46 in, so the square side is 50.91 in. That fits on 60 in wide fabric, so buy 50.91 in of fabric, rounded up to 1.50 yd. On 45 in fabric the same square does not fit, so this calculator splits the skirt into two halves and the estimate becomes 4.00 yd.
What is the difference between a full, half, and quarter circle skirt?
It is the fraction of a full circle used: full (360 deg) has the most flare and uses the most fabric; half (180 deg) is sewn from two D-shaped panels with moderate flare; quarter (90 deg) uses four panels and has the least flare. For a 28 in waist and 20 in length: full circle needs waist radius 4.46 in and about 1.50 yd on 60 in fabric; quarter circle needs waist radius 17.83 in and about 4.38 yd, because its narrower arc forces a much larger radius to fit the same waist.
Where do seam allowances go on a circle skirt pattern?
Allowances sit outside the seamlines. The waist cutting radius is the seamline radius minus the waist seam allowance (example: 4.46 in - 0.625 in = 3.83 in for a 28 in waist full circle). The outer cutting radius is the seamline radius plus the finished length plus the hem allowance (4.46 in + 20 in + 1 in = 25.46 in). Straight-edge allowances for multi-panel skirts extend only the radial edges, never the radii.
Can you show a worked metric example?
Yes. Waist 75 cm, full circle, finished length 60 cm, 1.5 cm waist and 2.5 cm hem allowances, 150 cm fabric: waist seamline radius = 75 / (2 x pi) = 11.94 cm; waist cut radius = 11.94 - 1.5 = 10.44 cm; outer cut radius = 11.94 + 60 + 2.5 = 74.44 cm; fabric square side = 148.87 cm, which fits on 150 cm fabric - buy 150.00 cm (the 148.87 cm raw need rounded up to the next 5 cm). Finished hem circumference = 2 x pi x (11.94 + 60) = 451.99 cm.
How do I calculate a three-quarter circle skirt?
Use fraction f = 0.75, so r = W / (1.5 x pi). Example: 28 in waist, 22 in length, 5/8 in waist and 1 in hem allowances: r = 28 / (1.5 x pi) = 5.94 in; outer cut radius = 5.94 + 22 + 1 = 28.94 in; finished hem arc = 1.5 x pi x (5.94 + 22) = 131.67 in; estimated fabric on 60 in width = 1.50 yd.
What size do I cut the waistband?
The waistband is a rectangle: length = finished waist + 2 x seam allowance (one at each end), height = 2 x (band width + seam allowance) so it folds in half. Example: 28 in waist, 2 in wide band, 1/2 in allowances: cut 29.00 in x 5.00 in. The waistband is included in the fabric estimate when you enable it (the 28 in waist example still buys 1.50 yd because the band nests beside the skirt).
What if my fabric is only 45 in wide?
A full circle whose square (2 x outer cut radius) is wider than the fabric is cut as two half-circles sewn at the side seams. Example: 28 in waist, 30 in long full circle: outer cut radius = 35.46 in, so the square would be 70.91 in - too wide for 45 in fabric. Two halves are packed instead: raw need 141.83 in, buy 4.00 yd. The calculator flags this with a two-piece note.
What is the hem circumference of a circle skirt?
Finished hem arc = sector angle x (waist radius + finished length). For the 28 in waist, 20 in long full circle example: 2 x pi x (4.46 + 20) = 153.66 in of hem to finish. For the same measurements as a half circle (30 in waist, 24 in length example): pi x (9.55 + 24) = 105.40 in.
Why does the calculator reject my seam allowance?
If the waist seam allowance is as large as the waist radius itself, the cut curve would reach or pass the center point - there is no waist hole left. Example: a 5 in allowance on a 28 in waist full circle (radius 4.46 in) is rejected. Reduce the allowance or recheck the waist measurement.
Does the calculator include wearing ease?
Yes. The radius uses waist + ease, so enter your body waist and add ease separately (1-2 in / 2-5 cm is typical so the skirt slips over the hips). Example: a 26 in body waist with 2 in ease is computed exactly like a 28 in waist: r = 28 / (2 x pi) = 4.46 in for a full circle.
What assumptions does this calculator make?
Four explicit ones. (1) Geometry: the skirt is an annular sector and the waist arc length equals waist + ease, giving r = W / (2 x pi x f) - the same convention used by major sewing pattern references. (2) Seam allowances sit outside the seamlines. (3) Fabric is plain (no nap or directional print), so pieces may be rotated when packing, and yardage is a conservative bounding-box estimate - always muslin-test expensive fabric. (4) Stretch fabrics behave differently: the waist hole can grow, so consider less ease and interface the waistband.
Free tool by NRTechStudio