Quick answer
For a full circle skirt, the waist radius is waist ÷ 2π and the outer radius is that plus the skirt length. A 28-inch waist and 20-inch length give radii of 4.456 and 24.456 inches, so the fabric needs a square of about 48.91 × 48.91 inches.
Enter the waist measurement, the length and the type of skirt (full, half or quarter circle). The calculator returns the radii and the fabric square.
Related tools: Circle Calculator: Radius, diameter, circumference and area of a circle from any one of them. Area of a Circle Calculator: Area of a circle from its radius, diameter or circumference. Circle Diameter Calculator: Diameter of a circle from radius, circumference or area.
How to use the Circle Skirt Calculator
- Enter waist measurement (in) (above 0).
- Enter skirt length (in) (above 0).
- Choose skirt: Full circle, Half circle and Quarter circle.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Waist measurement | A number, in in | > 0 |
| Skirt length | A number, in in | > 0 |
| Skirt | Choose one: Full circle; Half circle; Quarter circle | Starts at Full circle |
Formula and method
Formula
full: r = waist ÷ 2π; half: waist ÷ π; quarter: 2 × waist ÷ π; outer radius = r + length
IEEE-754 double precision; shown to the decimals indicated.
Add seam and hem allowances and ease to the result.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Waist measurement = 28; Skirt length = 20; Skirt = Full circle.
| Result | Value |
|---|---|
| Waist radius | 4.456 in |
| Outer radius | 24.456 in |
| Minimum fabric (single layer) | 48.91 × 48.91 in |
Example 2
Inputs: Waist measurement = 32; Skirt length = 24; Skirt = Half circle.
| Result | Value |
|---|---|
| Waist radius | 10.186 in |
| Outer radius | 34.186 in |
| Minimum fabric (single layer) | 68.37 × 34.19 in |
Example 3
Inputs: Waist measurement = 26; Skirt length = 18; Skirt = Quarter circle.
| Result | Value |
|---|---|
| Waist radius | 16.552 in |
| Outer radius | 34.552 in |
| Minimum fabric (single layer) | 34.55 × 34.55 in |
The first line is the headline result (waist radius). Below it the circle Skirt Calculator lists outer radius and minimum fabric (single layer), which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
The math
Full circle: r = waist ÷ 2π. Half circle: waist ÷ π. Quarter circle: 2 × waist ÷ π. The outer radius adds the length. Quarter circles fit in a smaller square of fabric but hang with less fullness.
Practical allowances
Add a seam allowance and hem allowance to the radii. Fabric with a nap or directional print may need more. The quoted fabric is for a single layer cut; check pattern layouts for fabric width.
How the result changes with waist measurement
Holding every other input at the first worked example, this table changes only waist measurement. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Waist measurement | Waist radius | Outer radius | Minimum fabric (single layer) |
|---|---|---|---|
| 14 | 2.228 in | 22.228 in | 44.46 × 44.46 in |
| 28 | 4.456 in | 24.456 in | 48.91 × 48.91 in |
| 56 | 8.913 in | 28.913 in | 57.83 × 57.83 in |
| 112 | 17.825 in | 37.825 in | 75.65 × 75.65 in |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Waist measurement: entering "0" shows "Waist measurement must be greater than 0." beside that field and no result.
- Skirt length: entering "0" shows "Skirt length must be greater than 0." beside that field and no result.
Choosing between the Circle Skirt Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Circle Calculator](/math/circle-calculator/) | i know the and value | Area |
| [Area of a Circle Calculator](/math/area-of-a-circle/) | i know the and value | Area |
| [Circle Diameter Calculator](/math/circle-diameter/) | i know the and value | Diameter |
| [Circle Perimeter Calculator](/math/circle-perimeter/) | radius | Circle Perimeter |
| [Circle Equation Calculator](/math/circle-equation/) | centre x, centre y and radius | Standard form |
Assumptions and limitations
- Seam allowances are not included
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for waist measurement and skirt length to confirm this.
Frequently asked questions
Which skirt uses the least fabric?
The quarter circle skirt uses the least fabric, but it also has the least fullness.
How do I mark the circle?
Pin a string at the centre and swing a marker at the radius.
Do I add a waistband?
Yes, cut the waistband separately; it is not part of the circle measurements.
What does the Circle Skirt Calculator calculate?
Waist radius and fabric needed for a full, half or quarter circle skirt. It returns Waist radius, Outer radius and Minimum fabric (single layer).
What formula does the Circle Skirt Calculator use?
full: r = waist ÷ 2π; half: waist ÷ π; quarter: 2 × waist ÷ π; outer radius = r + length. Add seam and hem allowances and ease to the result.
What do I need to enter in the circle Skirt Calculator?
You enter Waist measurement (in), Skirt length (in) and Skirt.
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Seam allowances are not included.
What does the “Skirt” option change?
It sets how the circle Skirt is worked out. The choices are Full circle, Half circle and Quarter circle.
What is an example of a circle Skirt result?
With waist measurement 28, skirt length 20 and skirt Full circle, the waist radius is 4.456 in.
Related calculators
- Circle Calculator — Radius, diameter, circumference and area of a circle from any one of them.
- Area of a Circle Calculator — Area of a circle from its radius, diameter or circumference.
- Circle Diameter Calculator — Diameter of a circle from radius, circumference or area.
- Circle Perimeter Calculator — Perimeter (circumference) of a circle from its radius.
- Circle Equation Calculator — Equation of a circle from its centre and radius.
- Unit Circle Calculator — Coordinates on the unit circle for an angle.
Sources
- OpenStax, Prealgebra 2e (Rice University): perimeter, area, volume, circumference and the Pythagorean theorem
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.