Circle Skirt Formula
To find the radius of a circle you need the following formula:
Circumference ÷ 2π
Example For Finding The Radius
Let’s use a 110cm waist as an example,
Circumference = 110cm 2π is: 2×3.14 which is = 6.28
110cm ÷ 6.28 = 17.52cm
Lets do the same but in inches
- Circumference = 44 inches
- 2π is: 2×3.14 which is = 6.28
- 44 ÷ 6.28 = 7 inches
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
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
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
One Third Circle Skirt Formula (120º)
Your formula for a one third circle skirt is:
