Circle Skirt Calculator: Waist Radius and Fabric

This circle skirt calculator works out the two numbers you need to draft a circle skirt: the radius of the waist curve and the radius of the hem. It also works out how much fabric to buy for the width of fabric you have.

It gives the length of the finished hem edge too, which is handy for buying binding, lace or trim.

A circle skirt is a ring of fabric. The inner edge becomes the waist and the outer edge the hem. The trick is that you cannot measure the radius of a waist; you measure its circumference, and the calculator works backwards to the radius with a little geometry. A full circle skirt uses a whole ring, a half circle skirt half a ring and a quarter circle skirt a quarter, so the same waist needs a larger radius as the skirt gets less full.

Measure in inches or centimetres. The fabric to buy is rounded up to the next eighth of a yard or ten centimetres, which is how most shops cut.

1. Choose inches or centimetres.
2. Enter your waist where the skirt will sit, and the finished length from waist to hem.
3. Choose a full, half or quarter circle.
4. Enter the usable width of your fabric.
5. Enter your waist seam allowance and hem allowance if your pattern adds them, or leave them at zero.
6. Read the two radii at the top, and the cutting radii, hem length, fabric length and layout below.

The presets show the default skirt on 60 inch fabric, as a half circle, and a metric full circle with seam and hem allowances.

1. Find the waist radius. The waist edge is the arc of a circle. For a full circle its length is 2πr, for a half circle πr and for a quarter circle πr/2. Setting that equal to your waist gives the radius.

1. Find the cutting radii. The waist is cut at the waist radius less the seam allowance, so the stitched seam lands on the waist line. The hem is cut at the waist radius plus the finished length plus the hem allowance.

1. Find the finished hem edge. The arc at the waist radius plus the length, for the fraction of a circle you chose.

1. Lay it out on the fabric. With R the hem cutting radius and W the fabric width: a full circle fits in one piece when 2R is no more than W, using 2R of fabric; otherwise, if R fits, it is cut as two half circles end to end, using 4R. A half circle uses R when 2R fits the width and 2R when only R fits. A quarter circle uses R when R fits. Anything wider is reported as not possible in one width.

1. Round the fabric to buy. The fabric length is converted to yards or metres and rounded up to the next 1/8 yard or 10 centimetres.

The default is a 28 inch waist, 20 inch length, full circle, 44 inch fabric, with no allowances:

1. Waist radius: 28 ÷ 2π = 4.46 inches.
2. Hem radius: 4.46 + 20 = 24.46 inches.
3. Finished hem: 2π × 24.46 = 153.7 inches of hem to finish.
4. Layout: the full circle is 48.91 inches across, wider than 44 inch fabric, but its radius fits, so it is cut as two half circles end to end: 97.83 inches of fabric.
5. To buy: 2.75 yards.

On 60 inch fabric the full circle fits in one piece, and 1.375 yards is enough. As a half circle, the same waist needs an 8.91 inch radius and a 28.91 inch hem radius, and takes 1.625 yards of 44 inch fabric.

A metric full circle for a 70 centimetre waist, 50 centimetres long, on 150 centimetre fabric with a 1.5 centimetre seam and a 2 centimetre hem, has an 11.14 centimetre waist radius, cut at 9.64, and a hem cut at 63.14. It takes 1.3 metres.

Divide your waist by 2π (about 6.28) for a full circle, by π (about 3.14) for a half circle, or by π/2 (about 1.57) for a quarter circle. A 28 inch waist gives 4.46, 8.91 and 17.83 inches. The table below lists the radius for waists from 22 to 44 inches in all three styles.

It depends on the hem radius and the fabric width. A full circle needs a square of fabric twice the hem radius on each side, which only the widest fabrics can supply; on narrower fabric it is cut as two halves, which takes twice the length but adds side seams. A half or quarter circle uses much less.

Enter your fabric width and the calculator chooses the layout and the length.

• Seam allowances on side seams. When a full circle is cut as two halves, each straight edge needs a seam allowance, which this layout does not add.
• Waistband and closure. A zip or placket and the waistband are drafted separately.
• Stretch and ease. The waist is used exactly as entered. Add ease for a woven fabric, or subtract for a knit, before entering it.
• Directional prints and nap. Fabric with a one-way print or a nap may need a different layout and more length.
• Dropping on the bias. Circle skirts hang on the bias in places and the hem can drop; many sewists let the skirt hang before levelling the hem.

• Using the waist as the radius. The radius is the waist divided by 2π for a full circle, not the waist itself.
• Forgetting the seam allowance at the waist. If the waist curve is cut exactly on the waist radius and then sewn with a seam allowance, the skirt comes out too big. Enter the allowance and cut at the smaller radius.
• Measuring length from the wrong place. Length runs from the waist seam to the hem, not from the waistband top.
• Assuming one piece will fit. Check the fabric width: most full circle skirts need wider fabric than you expect.

• NIST Handbook 44, Appendix C, General Tables of Units of Measurement: the inch, the yard, and the conversion to centimetres. nist.gov/pml/owm/nist-handbook-44-current-edition
• NIST Handbook 130 (2025), Uniform Packaging and Labeling Regulation, section 6.9: bi-dimensional goods such as fabric declared by length and width. doi.org/10.6028/NIST.HB.130-2025