Circle skirt calculator: waist radius and fabric
A circle skirt is a flat ring of cloth, so two numbers describe it: the waist radius (the hole in the middle) and the outer radius (the hem). This circle skirt calculator works both out from your waist and skirt length for full, half and quarter circle skirts, draws the shape, and estimates the fabric to buy.
It works in centimetres or inches, adds the ease, hem and seam allowances you choose, and gives a waistband strip. It runs in your browser; use it for adults and for children by entering the child’s own measurements.
How to use the Circle Skirt Calculator
- Pick full, half or quarter circle and your unit.
- Enter your waist and the skirt length from waist to hem.
- Adjust ease, hem allowance, waist seam allowance and waistband height if you want different values.
- Enter the fabric width and read the radii and the metres to buy.
- Copy the working; mark the inner and outer arcs on the cloth with a string and pin or a tape measure.
Circle Skirt Calculator features
Three shapes
Full circle (360°), half circle (180°) and quarter circle (90°); a gentler shape uses less fabric.
Exact radii
The waist radius follows from r = waist ÷ angle in radians.
Fabric layouts
One piece, nested halves or stacked halves, depending on how wide your cloth is.
Drawn shape
A scaled sketch of the ring or sector shows what you will cut.
The formulas
These are geometry, so they do not depend on a source; the ease, hem and seam defaults (2 cm, 1.5 cm and 1.5 cm) and the three-inch waistband overlap are this page’s own choices and are editable. Gathered or elasticated waists can use more ease. Quarter circle skirts are narrower and sit closer to the body, full circles have the most swing and use the most cloth.
- The waist edge of a sector of angle θ is an arc of length θ × r, so r = waist ÷ θ with θ in radians.
- Full circle: r = waist ÷ 2π, about waist × 0.159. Half circle: r = waist ÷ π, about waist × 0.318. Quarter circle: r = 2 × waist ÷ π, about waist × 0.637.
- Outer radius R = r + skirt length + hem allowance. The waist seam allowance is taken off the inner radius, because it sits above the stitching line.
| Waist 72 cm incl. ease | Waist radius r | Outer radius R (55 cm length, 1.5 cm hem) |
|---|---|---|
| Full circle | 11.5 cm | 68.0 cm |
| Half circle | 22.9 cm | 79.4 cm |
| Quarter circle | 45.8 cm | 102.3 cm |
How the fabric length is estimated
The skirt is treated as its bounding box. A full circle needs a square 2R across; if the cloth is that wide, buy 2R. On narrower cloth the skirt is cut as two half circles with side seams: nested head to tail they need cloth at least 1.74R wide and 3R of length; stacked they need R of width and 4R of length. A half circle needs R along the grain on cloth 2R wide, otherwise 2R. A quarter circle needs R.
The waistband is a strip as long as the waist plus ease, a 3 in overlap and seams; its width adds to the layout length. The total is rounded up to the next 0.1 m. If the fabric is narrower than R the page says so rather than guessing. For other garments see the fabric calculator for clothing; to change units use the length converter.
Tips for kids and drape
For children, measure the waist and length directly and use plenty of ease or an elastic waist, because children grow and need to pull skirts on. Circle skirts hang on the bias around much of the hem, so the hem stretches; hang the skirt for a day and then level and trim the hem.
Circle Skirt Calculator FAQ
How do you calculate the radius of a circle skirt?
Divide the waist measurement by 2π (6.283) for a full circle, by π (3.142) for a half circle, and multiply 2 × waist ÷ π for a quarter circle. Then add the skirt length and hem for the outer radius.
How much fabric do I need for a circle skirt?
A full circle needs about twice the outer radius if the cloth is that wide. With a 72 cm waist and a 55 cm skirt that is about 1.5 m of 140 cm cloth.
Which is better, a half or full circle skirt?
A full circle has the most swing and uses the most cloth; a half circle is less full and uses less; a quarter circle is closest fitting.
Should I add ease to the waist?
Yes, unless the skirt has an elastic waist. The calculator adds 2 cm by default; change it to suit your zip or fastening.
Can I use this for a child’s circle skirt?
Yes. Enter the child’s waist and skirt length and add more ease or use an elastic waist.
Why does my circle skirt hem look uneven?
The hem falls on the bias in places and stretches. Let the skirt hang for a day, then trim the hem level before turning it up.