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Circle Skirt Formulas: Calculate Your Circle Skirt Radius!

Want to make a circle skirt for yourself? This quick guide to circle skirt formulas will help you make your own circle skirt in no time! remember that the circumference is the waistline on a circle skirt and you’re all set!

The five most used circle skirt formulas are:

  1. Full circle skirt: C = 2πr
  2. Half circle skirt: 2C ÷ 2π
  3. Three quarter circle skirt: 1.3C ÷ 2π
  4. Third circle skirt: 3C ÷ 2π
  5. Quarter circle skirt: 4C ÷ 2π

Below are full explanations and workings on these circle skirt formulas, but for any that don’t make sense, I have a circle skirt measurement chart at the bottom in both inches and centimetres for you to use!

If you feel quite confident, you can then draft a full circle skirt pattern here!

Circle skirt formulas

Formula For The Radius Of A Circle

You only need two measurements to make a circle skirt formula work for you:

  • Your waist measurement (known as circumference)
  • Pi, also viewed as π (which is 3.14 rounded from 3.141592653589793238462)

Here’s the basic formula for a circle’s circumference:

C = 2πr

Circle skirt formulas use the radius of a circle for the waist circumference and another for the hem circumference, but because peeps get confused with all the numbers and terms, let’s break it down more simply so it’s less confusing.

To find the radius of a circle you need the following formula:

Circumference ÷ 2π

Example For Finding The Radius

Let’s use my waist as an example, which was 110cm:

  • Circumference = 110cm
  • 2π is: 2×3.14 which is = 6.28
  • 110cm ÷ 6.28 = 17.52cm

Lets do the same but in inches for those North American readers:

  • Circumference = 44 inches
  • 2π is: 2×3.14 which is = 6.28
  • 44 ÷ 6.28 = 7 inches

Full Circle Skirt Formula (360º)

I did cover the full circle skirt in full for anyone ready to draft that pattern. But, here’s the formula for a full circle skirt:

Waist for a full circle skirt = C (+SA) ÷ 2π

If I were making a full circle skirt I would use the above formula (as shown in the example further up) but would also need to factor in the number of seams and the seam allowance amount (I usually use 1cm per seam, and I have two seams with one on each side of the skirt, which would be a total of 4 raw edges) before running the formula:

  • 110cm (C) + 4cm (4xSA) = 114cm
  • 2π = 2×3.14 = 6.28
  • 114 ÷ 6.28 = 18.15cm

You’ll also want to subtract an amount for the waistline seam allowance, for finishing the waist with a facing, or a waistband of some sort:

  • 18.15cm – 1cm = 17.15cm

This is how it looks for me in inches:

  • 44 inches (C) + 2 inches (4xSA) = 46 inches
  • 2π = 2×3.14 = 6.28
  • 46 ÷ 6.28 = 7.3 inches (r)
  • 7.3 – 0.5 (waist SA) = 6.8 inches
Circle skirt formula for the full circle skirt!

Half Circle Skirt Formula (180º)

The half circle skirt uses our waist circumference in a semi-circle rather than the full circle we used in the formula above! This means we need to double our waist measurement to find the right radius! Here’s the basic formula for a half circle skirt:

Waist for a half circle skirt = 2C (+SA) ÷ 2π

Lets use me as an example again:

  • C = 110cm
  • 2C = 2x 110cm = 220cm
  • Number of seams = 2
  • Amount for seam allowance = 1cm
  • Total raw seam edges = 4
  • SA = 4x 1cm = 4cm
  • 220cm + 4cm = 224cm
  • 2π = 2x 3.14 = 6.28
  • R = 224 ÷ 6.28 = 35.67cm
  • Finally, subtract the waistband seam allowance amount (1cm) = 34.67cm
Circle skirt formula for the half circle skirt!

I wrote a tutorial after making an easy half circle skirt one with pockets and an elastic waistband if you’d like to see a half circle skirt in action!

Three Quarter Circle Skirt Formula (270º)

Your formula for a three quarter circle skirt is:

Waist for a three quarter circle skirt = 1.3C (+SA) ÷ 2π

Lets use the same measurements as before so you see the continuity in the changes of numbers!

  • C = 110cm
  • 1.3C = 1.3 x 110cm = 143cm
  • Number of seams = 2
  • Amount for seam allowance = 1cm
  • Total raw seam edges = 4
  • SA = 4x 1cm = 4cm
  • 143cm + 4cm = 147cm
  • 2π = 2x 3.14 = 6.28
  • R = 147 ÷ 6.28 = 23.4cm
  • Finally, subtract the waistband seam allowance amount (1cm) = 22.4cm
Circle skirt formula for the three quarter circle skirt!

One Third Circle Skirt Formula (120º)

Your formula for a one third circle skirt is:

Waist for a one third circle skirt = 3C (+SA) ÷ 2π

I feel like this is all probably making sense for you now?

  • C = 110cm
  • 3C = 3x 110cm = 330cm
  • Number of seams = 2
  • Amount for seam allowance = 1cm
  • Total raw seam edges = 4
  • SA = 4x 1cm = 4cm
  • 330cm + 4cm = 334cm
  • 2π = 2x 3.14 = 6.28
  • R = 334 ÷ 6.28 = 53.18cm
  • Finally, subtract the waistband seam allowance amount (1cm) = 52.18cm
Circle skirt formula for the one third circle skirt!

Quarter Circle Skirt Formula (90º)

Finally, your formula for a one quarter circle skirt is:

Waist for a quarter circle skirt = 4C (+SA) ÷ 2π

  • C = 110cm
  • 4C = 4x 110cm = 440cm
  • Number of seams = 2
  • Amount for seam allowance = 1cm
  • Total raw seam edges = 4
  • SA = 4x 1cm = 4cm
  • 440cm + 4cm = 444cm
  • 2π = 2x 3.14 = 6.28
  • R = 444 ÷ 6.28 = 70.70cm
  • Finally, subtract the waistband seam allowance amount (1cm) = 69.70cm
Circle skirt formula for the one quarter circle skirt!

As promised, below are the printable measurement charts for the five different circle skirts. These have a seam allowance included as follows:

  • Inches: 2 side seams (4 raw edges) each with a half inch allowance, and a ½ inch allowance for the waistline seam allowance
  • Centimetres: 2 side seams (4 raw edges) each with a 1cm seam allowance and a 1cm allowance for the waistline seam allowance

Phew. Enjoy – and let me know how you get on with them!

Want to read more?

Circle skirt formulas - the measurements needed for your circle skirt radius in centimetres!
Circle skirt formulas - the measurements needed for your circle skirt radius in inches!

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