Circle skirt calculator: waist radius, hem and fabric for full, half and quarter
This circle skirt calculator turns your waist measurement into the radius you draw on the fabric. The waist becomes the inner circle (or part of it), so its radius is waist ÷ 2π for a full circle skirt. A 28 in waist gives a waist radius of 4.46 in; with a 24 in skirt length the hem radius is 28.46 in.
Example: Unit: inches · Skirt type: full circle (360°) · Waist measurement 28 · Skirt length 24 → Waist radius: Waist radius 4.46 in. Source: OpenStax, Prealgebra 2e, section 9.5 “Use Properties of Circles”: diameter d = 2r, circumference C = 2πr (read 09.10.2026). Updated: .
How it is calculated
Waist radius = waist × (360 ÷ angle) ÷ 2π. A circle’s circumference is C = 2πr. In a full circle skirt the waist is the whole inner circle, so r = waist ÷ 2π (about waist ÷ 6.28). A half circle skirt uses only half the circle for the waist, so its radius doubles: r = waist ÷ π. The hem radius is the waist radius plus the skirt length.
Examples for a 28 in waist and 24 in length
| Skirt | Waist radius | Hem radius | Hem width |
|---|---|---|---|
| Full circle | 4.46 in | 28.46 in | 178.80 in |
| 3/4 circle | 5.94 in | 29.94 in | 141.10 in |
| Half circle | 8.91 in | 32.91 in | 103.40 in |
| Quarter circle | 17.83 in | 41.83 in | 65.70 in |
In centimeters: a 72 cm waist gives 11.46 cm for a full circle and 22.92 cm for a half circle.
How much fabric?
The pattern piece of a full or 3/4 circle skirt fits in a square of 2R × 2R, a half circle in 2R × R and a quarter circle in R × R. For the 28/24 in full circle skirt that is 56.91 × 56.91 in – wider than most fabrics, so it is usually cut in two or four panels with seams. Fabric for curtains is in the curtain fabric calculator; radius, diameter and circumference in the circle calculator.
Frequently asked questions
How do you calculate the waist radius of a circle skirt?
Divide the waist by 2π (6.283). A 28 in waist gives 4.46 in, a 72 cm waist 11.46 cm.
What is the formula for a half circle skirt?
Waist ÷ π. A 28 in waist gives a radius of 8.91 in.
How wide is the hem of a full circle skirt?
2π × (waist radius + length). For 28 in waist and 24 in length: 178.80 in.
How much fabric do I need for a circle skirt?
The full circle fits in a square of twice the hem radius: 56.91 × 56.91 in for the example – usually cut in panels.
Should I add seam allowance?
Yes. The calculator gives the finished lines; add seam allowance at the waist and hem allowance at the hem.
What is a quarter circle skirt?
A skirt whose waist forms a 90° arc: radius = 2 × waist ÷ π, 17.83 in for a 28 in waist – less flare, less fabric.
Sources and legal basis
As of: · Editorial policy
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