How do I calculate the inner radius for a circle skirt?

For a full circle skirt, the inner radius equals your waist measurement divided by (2 x pi), which is approximately 6.2832. For a half circle skirt, divide the waist by pi. For a quarter circle skirt, divide the waist by (pi / 2). Adding a seam allowance of 1 to 1.5 cm to the inner radius is recommended before cutting.

How much fabric do I need for a circle skirt?

The fabric you need depends on the circle type and your measurements. For a full circle skirt, you need a square of fabric at least as wide and tall as twice the outer radius (inner radius plus skirt length). The outer radius plus a seam allowance gives you the cutting radius. For example, a full circle skirt with a 70 cm waist and 60 cm length needs a fabric square of approximately 145 cm x 145 cm (before adding seam allowances). Fabric area without seam allowances is about 1.55 square metres.

What is the difference between a full, half, and quarter circle skirt?

A full circle skirt uses a complete 360-degree circle and creates the most flare and volume. A half circle skirt uses 180 degrees (two mirror-image pieces sewn together) and has moderate flare with less fabric. A quarter circle skirt uses 90 degrees (four pieces) and sits closer to the body with less flare. All three styles use the same inner radius formula, adjusted by the fraction of the circle being used.

Circle Skirt Calculator

Enter your waist measurement and desired skirt length to calculate the inner radius, outer radius, cutting diameter, and fabric area needed. Supports full circle, half circle, and quarter circle skirts.

Add a seam allowance to the inner and outer radius before cutting. Measurements can be entered in centimetres or inches.

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Verified June 2026 Standard circle skirt geometry: inner radius = waist / (2π x circle fraction).

1. Measurements

Unit of measurement

Waist measurement (cm)

Skirt length (cm)

Seam allowance (cm each edge)

2. Skirt Style

Circle type

Number of panels

Circle Skirt Cutting Dimensions

Inner Radius
-
Waist curve radius

Outer Radius

Hem curve radius

Cutting Diameter

Fabric square needed

Fabric Area

Net skirt area (no SA)

Cutting Dimensions (including seam allowance)

Circle type-

Waist measurement-

Skirt length-

Seam allowance-

Inner radius (no SA)-

Inner radius (with SA)-

Outer radius (no SA)-

Outer radius (with SA)-

Fabric square to buy-

Fabric and Panels

Number of panels-

Angle per panel-

Net skirt fabric area-

Hem circumference-

Waist circumference (cut)-

Waste from corners-

Gross fabric per panel-

Tip: Enter your measurements above.

How a Circle Skirt is Constructed

A circle skirt gets its flare from the geometry of a circle. The waist opening forms an inner arc and the hem forms a larger outer arc. When laid flat, the pattern piece is an annulus (a ring shape) or a fraction of one, depending on the style chosen.

The key measurement is the inner radius: the radius of the waist hole in the fabric. This is calculated directly from the waist circumference and the fraction of a circle being used.

The Formula

For a full circle skirt, the inner circumference must equal the waist measurement:

Inner radius (r) = waist / (2 x pi)

For a half circle skirt, the waist is divided between two pieces, so each piece contributes half the waist circumference:

r = waist / (2 x pi x 0.5) = waist / pi

For a quarter circle skirt (four pieces), each piece contributes a quarter:

r = waist / (2 x pi x 0.25) = 2 x waist / pi

Once you have the inner radius, the outer radius is simply:

Outer radius (R) = r + skirt length

The fabric area for the finished skirt (without seam allowances) is:

Area = pi x (R squared - r squared)

The fabric square you need to buy is at least 2R x 2R (for a full circle in one piece), or 2R x R (for a half circle per panel), with seam allowances added.

Worked Example

Using the default values: waist = 70 cm, skirt length = 60 cm, full circle, 1 panel, seam allowance = 1.5 cm.

Step	Calculation	Result
Inner radius (no seam allowance)	70 / (2 x 3.14159)	11.14 cm
Outer radius (no seam allowance)	11.14 + 60	71.14 cm
Inner radius (with 1.5 cm SA)	11.14 - 1.5	9.64 cm
Outer radius (with 1.5 cm SA)	71.14 + 1.5	72.64 cm
Fabric square needed	2 x 72.64	145.28 cm x 145.28 cm
Net skirt area	pi x (71.14^2 - 11.14^2)	approx. 15,510 cm^2 = 1.55 m^2

When cutting, fold the fabric in quarters and place the inner corner at the fold point. Use a piece of string or a ruler to mark the inner arc at the inner radius and the outer arc at the outer radius. Cut along both arcs, then unfold to reveal the full ring.

Seam Allowances

Add your seam allowance to the outer radius (for the hem seam) and subtract it from the cutting measurement for the waist (so the inner radius on the pattern is smaller by the seam allowance, since you are cutting from the outside). A seam allowance of 1 to 1.5 cm is standard for most sewing projects. This calculator adds the seam allowance to the outer radius and subtracts it from the inner cutting radius so the finished garment matches your measurements.

Choosing Your Circle Type

Style	Circle fraction	Flare	Fabric used	Pieces to cut
Full circle	360 degrees (1 full)	Maximum	Most	1 (or 2 half-rings)
Half circle	180 degrees (1/2)	Moderate	Medium	2
Quarter circle	90 degrees (1/4)	Minimal	Least	4

Related Calculators

Maths and Stats Calculators
Area of a Circle Calculator
Annulus Calculator: area and perimeter of a ring shape.
Arc Length and Sector Area Calculator
Area Calculator

Method: Standard circle skirt geometry. Inner radius derived from waist circumference using the formula r = waist / (2 x pi x circle_fraction). Fabric area calculated as the annulus area: pi x (R^2 - r^2). Seam allowance added to the outer radius and subtracted from the inner cutting radius.

This calculator provides pattern dimensions based on standard geometric formulas. Fabric requirements may vary depending on fabric width, layout, and any additional design elements such as pockets or waistbands. Always verify measurements with a test piece before cutting your final fabric.