Bias Tape Calculator
Calculate bias strip cut width, continuous bias fabric square dimensions, and bolt yardage for single-fold or double-fold bias tape.
Open toolCircle Skirt Calculator
Select your unit and skirt fullness (Full, 3/4, Half, or Quarter circle) and enter your waist, length, and seam allowances in the Circle Skirt Calculator below to get your exact waist cutting radius, outer hem cutting radius, and hem sweep.
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Enter the inputs, then select Calculate Skirt Pattern.
Your result
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Result will appear here
How Circle Skirt Calculator works
The Circle Skirt Calculator divides your waist measurement by the arc fraction (2*pi*k) to find the stitched waist radius, subtracts your waist seam allowance to find the raw cutting radius from the corner fold, and adds your skirt length plus seam and hem allowances for the outer arc.
Stitched R_waist = Waist / (2 * pi * k); Cut R_waist = Stitched R_waist - Seam; Cut R_hem = Cut R_waist + Length + Seam + Hem.
If you include a vertical zipper or side seam, the exported notes also show the radius adjustment when adding seam allowances to the straight edges.
Circle Skirt Calculator Quick Reference & Input Guide
Review the input parameters, allowed value ranges, and worked reference cases for the Circle Skirt Calculator below before running your calculation.
| Parameter / Scenario | Default / Sample Value | Rule or Allowed Range | Output / Usage Note |
|---|---|---|---|
| Input: Measurement unit | in | Options: Inches (in), Centimeters (cm) | Required workspace parameter |
| Input: Circle skirt fullness | full | Options: Full Circle Skirt (360 deg), Three-Quarter Circle Skirt (270 deg), Half Circle Skirt (180 deg), Quarter Circle / A-Line Skirt (90 deg) | Required workspace parameter |
| Input: Finished waist (or hip for elastic pull-on) | 28 | Range: 10 to 250 | Required workspace parameter |
| Input: Finished skirt length (waist to hem) | 22 | Range: 4 to 150 | Required workspace parameter |
| Worked Case 1: Full Circle skirt (28 in waist, 22 in length, 0.625 in seam, 0.5 in hem) | Preloaded / test values | Waist Cut Radius (R_w) = (Waist / (2 * pi * Fraction)) - SeamAllowance; Outer Cut Radius (R_h) = R_w + SkirtLength + SeamAllowance + HemAllowance | Stitched waist radius is 28 / (2*pi) = 4.46 in. Subtracting 0.625 in seam allowance gives a 3.83 in Waist Cut Radius. Outer Hem Cut Radius is 3.83 + 22 + 0.625 + 0.5 = 26.96 in (requiring a 53.91 in fabric diameter and 166.25 in hem sweep). |
| Worked Case 2: Half Circle skirt (28 in waist, 22 in length, 0.625 in seam, 0.5 in hem) | Preloaded / test values | Waist Cut Radius (R_w) = (Waist / (2 * pi * Fraction)) - SeamAllowance; Outer Cut Radius (R_h) = R_w + SkirtLength + SeamAllowance + HemAllowance | With k = 0.5, stitched waist radius doubles to 8.91 in and Waist Cut Radius is 8.29 in. Outer Hem Cut Radius is 31.41 in with a 97.12 in finished hem sweep. |
How to use Circle Skirt Calculator step by step
Measure your waist (or full hips for a pull-on elastic waist) and desired skirt length from waist to knee or midi.
Choose unit and circle fullness (360, 270, 180, or 90 deg)
Select Inches or Centimeters and choose Full (360 deg), Three-Quarter (270 deg), Half (180 deg), or Quarter (90 deg) circle.
Enter waist measurement and finished skirt length
Input your waist circumference and desired finished length.
Set waist seam and hem allowances and calculate
Enter your waist seam allowance (e.g., 0.625 in = 5/8 in) and hem allowance (e.g., 0.5 in), then click Calculate Skirt Pattern.
Worked examples for Circle Skirt Calculator
Compare a 28-inch waist Full Circle skirt against a Half Circle skirt of the same length.
Full Circle skirt (28 in waist, 22 in length, 0.625 in seam, 0.5 in hem)
Stitched waist radius is 28 / (2*pi) = 4.46 in. Subtracting 0.625 in seam allowance gives a 3.83 in Waist Cut Radius. Outer Hem Cut Radius is 3.83 + 22 + 0.625 + 0.5 = 26.96 in (requiring a 53.91 in fabric diameter and 166.25 in hem sweep).
Half Circle skirt (28 in waist, 22 in length, 0.625 in seam, 0.5 in hem)
With k = 0.5, stitched waist radius doubles to 8.91 in and Waist Cut Radius is 8.29 in. Outer Hem Cut Radius is 31.41 in with a 97.12 in finished hem sweep.
Check outer radius against your fabric bolt width
A Full Circle skirt cut in one piece requires fabric at least 2 * Outer Hem Radius wide (53.9 in above). On narrower 44-inch fabric, cut two Half-Circle panels and join them with two side seams.
How to interpret the Circle Skirt Calculator output
Mark both the Waist Cut Radius and Outer Hem Cut Radius from the same corner pivot point on your folded fabric.
The headline result shows your Waist Cut Radius and Outer Hem Cut Radius. Breakdown cards list Stitched waist radius, Finished hem circumference (sweep, useful for buying bias tape or horsehair braid), Minimum single-piece fabric width, and Two-panel yardage estimate.
Input limits, assumptions, and related tools
Ensure the waist cut radius stays positive when using thick seam allowances on small waists.
Your waist seam allowance must be smaller than the stitched waist radius so the inner cut radius stays greater than zero. To calculate bias binding for your finished hem sweep, copy the Finished Hem Sweep value into the Bias Tape Calculator.
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Open toolCircle Skirt Calculator: common questions
Answers about using Circle Skirt Calculator and understanding its results.
Why is the waist seam allowance subtracted from the waist radius instead of added?
The waist opening is an inside curve. Cutting a smaller radius puts extra fabric inside the ring; when you stitch 5/8 inch (1.5 cm) further out from that cut edge, the stitched circle has a larger radius and longer circumference that matches your finished waist.
What is the formula for waist radius on Full, 3/4, Half, and Quarter circle skirts?
Let Fraction k be 1.0 (Full), 0.75 (Three-Quarter), 0.50 (Half), or 0.25 (Quarter). Stitched Waist Radius = Waist / (2 * pi * k). Subtract your waist seam allowance to get the raw Waist Cut Radius.
What if I am sewing an elastic pull-on waistband instead of inserting a zipper?
For a pull-on elastic skirt with no zipper opening, enter your widest full-hip measurement (plus 1 inch / 2.5 cm ease) into the 'Finished waist' box so the skirt can slide up over your hips before the elastic gathers it.
Why should a circle skirt hang for 24 hours before hemming?
A circle skirt rotates through true grain, cross-grain, and 45-degree bias. The bias sections stretch downward under gravity; letting the skirt hang on a dress form or hanger overnight lets you trim the uneven bias drop level before hemming.
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