Circle skirt calculator

The waist radius of a circle skirt is your waist plus a little ease, divided by 2π times the fraction of the circle: about waist ÷ 6.28 for a full circle and waist ÷ 3.14 for a half circle. Add the skirt length to that radius to get the hem radius. The calculator above does the arithmetic and checks the pieces against your fabric.

How do you calculate the waist radius of a circle skirt?

A circle skirt is a ring cut from fabric: the inner circle becomes the waist, the outer circle the hem. The inner circle has to measure your waist, so the radius is:

radius = (waist + ease) ÷ (2 × π × fraction)

The fraction is 1 for a full circle, 0.75 for three-quarter, 0.5 for half and 0.25 for quarter. The calculator adds 1 cm (3/8 in) of ease to the waist, the same as Sewly's own circle skirt pattern, so a waistband closes comfortably.

A worked example in centimeters and inches

For a full circle with a 72 cm waist: 72 + 1 = 73 cm, and 73 ÷ 6.28 = 11.6 cm. With a 60 cm skirt, the hem radius is 71.6 cm and the hem measures 4.5 m around, so plan a narrow hem.

In inches, a 28 in waist plus 3/8 in of ease gives a radius of 4 1/2 in. A 24 in skirt makes the hem radius 28 1/2 in and the hem about 179 in (5 yd) around.

The radius is measured on the stitching line. When you cut, take the seam allowance off the waist radius (the waist circle gets smaller) and add the hem allowance to the outer radius: the calculator shows both cutting radii. Staystitch the waist right after cutting, because part of it is on the bias and stretches easily.

How much fabric do you need for a circle skirt?

The pieces are laid on fabric folded selvedge to selvedge, with the center front on the fold. The calculator tries two layouts and keeps the shorter one that fits: front and back each cut on the fold with side seams, or the whole skirt in one piece on the fold with a seam at center back (possible for three-quarter, half and quarter circles). It leaves 1 cm at the selvedges and adds about 8 % plus 10 cm for shrinkage and squaring the ends, like the quantities in Sewly's patterns.

The limit is the folded width: the outer cutting radius has to fit in half the fabric width. A full circle 60 cm (24 in) long fits folded 150 cm (60 in) fabric only for a waist under about 80 cm (31 1/2 in), and never fits 140 cm (55 in) fabric. When a width is too narrow, the table shows the longest skirt that would fit: shorten the skirt, choose a half circle, or cut the pieces opened out on a single layer and add seams.

Tips before you cut

• Let the finished skirt hang for a day before hemming: the bias sections drop, and you trim the hem level afterwards.
• Light, drapey fabrics such as viscose challis, crepe or cotton lawn swing best; stiff fabrics stand away from the body.
• One-way prints and napped fabrics need every piece facing the same way, which can take more length.

For the full sewing steps, read how to sew a circle skirt cut to your waist. If you would rather skip the drafting, Sewly's circle skirt pattern uses this same formula with your measurements and adds the waistband, the sewing steps and the cutting layout.