Circle Skirt Calculator

Find the waist and hem radii

Calculate the waist seam radius, inner cut radius and outer cut radius for a full, half or quarter circle skirt. Enter the finished waist opening and skirt length, then add your chosen waist seam and hem allowances separately.

These measurements describe an ideal circular shape. Choose the finished waist opening with the ease your project needs; a body waist measurement alone does not decide the fit.

Use one unit for every measurement. Changing the unit converts the numbers already entered.

The intended opening at the waist seam, including any ease you have chosen.
From the waist seam to the finished hem; exclude a separate waistband.
Extends inward from the waist seam, making the cut radius smaller. Enter 0 if no allowance is needed.
The total fabric depth beyond the finished hem for your chosen finish. Enter 0 for a finish that needs no extra depth.

Enter your measurements and select Calculate radii.

The circle skirt formula

Let C be the finished waist circumference and f the circle fraction: 1 for a full circle, ½ for a half circle or ¼ for a quarter circle. The waist seam is an arc with length C = 2 × π × r × f.

Waist seam radius r = C ÷ (2 × π × f)
Inner cut radius = r − waist seam allowance
Outer cut radius = r + finished skirt length + hem allowance

The inner cut radius must be greater than zero. A waist allowance that equals or exceeds the waist seam radius leaves no valid inner cutting arc. All dimensions in a calculation must use the same unit; 1 inch equals 2.54 cm.

A worked example

For a 76 cm finished waist opening, 60 cm skirt length, 1 cm waist seam allowance and 2 cm hem allowance, the calculated radii are:

Example radii in centimetres, rounded to two decimal places
Circle type Waist seam Inner cut Outer cut
Full 12.10 cm 11.10 cm 74.10 cm
Half 24.19 cm 23.19 cm 86.19 cm
Quarter 48.38 cm 47.38 cm 110.38 cm

For the full circle, the equivalent measurements in inches give radii of approximately 4.76 in, 4.37 in and 29.17 in. Changing units does not change the intended shape.

Plan the construction around the geometry

Straight edge seam allowances, fastening overlaps, zipper extensions and separate waistband dimensions need their own drafting decisions. The radii do not add those features. A fixed waist opening also needs a way to pass the hips, such as a suitable fastening; elasticated construction requires different fit and waistband decisions.

Circular skirts include fabric on the bias. Allow the fabric to settle before checking and levelling the hem, following the fabric and construction guidance for your project. Make a fitting sample to check the opening, ease and length before cutting your final cloth.

These radii are a starting point for circular drafting. Fabric consumption depends on layout, fabric width, seams, grain, print direction and other pieces, so it cannot be established by the radii alone.

When you know the full cutting shapes, use the Fabric Yardage Calculator to plan their bounding rectangles across a usable fabric width. It gives a conservative single-layer layout; it does not nest curved circle-skirt pieces or replace a pattern’s cutting plan.

Continue planning your skirt

Use the size guide to distinguish body measurements from finished dimensions, and the printing and assembly guide when you work from a PDF pattern. Browse skirt sewing patterns to compare other silhouettes.

Sewlore’s 1950s Circle Skirt is a First Release pattern preparation order.