How to use the circle skirt calculator
- Enter your waist measurement and the finished skirt length from the waist seam to the bottom edge, in inches.
- Choose a full, three quarter, half or quarter circle. A smaller part of a circle hangs closer to the body with less fullness.
- Enter the fabric width between the selvages. The 45 inches shown is an example, so use your fabric.
- Open the options for the hem allowance, seam allowance and ease if you want to change the examples, then read the two cutting radii, the number of pieces and the yardage.
Formula
waist radius = (waist + ease) / (2 x pi x fraction of a circle)
inner cutting radius = waist radius - seam allowance
outer cutting radius = waist radius + length + hem allowance
fabric = rows of pieces x (outer cutting radius + seam allowance), rounded up to an eighth of a yard
The curved waist edge of the skirt is part of a circle whose arc length must equal the waist measurement. The fraction of a circle, from 1 for a full circle to 0.25 for a quarter, sets how large that circle is.
A full circle skirt for a 28 inch waist
For a 28 inch waist and a 22 inch length, the waist radius is 28 / (2 x pi) = 4.456 inches. With a 0.625 inch seam allowance and a 1 inch hem, the waist hole is cut at radius 3.831 inches and the outer edge at 27.456 inches. The hem edge is 2 x pi x (4.456 + 22) = 166.2 inches around.
The tool lays four quarter circle pieces, each in a square 28.08 inches on a side, on 45 inch fabric. Only one fits across, so four rows are needed, 112.3 inches, which rounds up to 3.125 yards.
A half circle skirt for a 30 inch waist with 1 inch of ease, 24 inches long, on 60 inch fabric needs a waist radius of 9.868 inches and an outer radius of 34.368 inches, and takes 2 yards.
How the yardage is worked out
The tool splits the circle into quarter circle pieces and places each piece in a square. It fits as many squares across the fabric as it can and counts the rows. That layout cuts one layer with no folds, so it often asks for more than a pattern does. Folding the fabric in half and in quarters, as most patterns show, can use noticeably less.
A waistband, a zipper, a directional print or a fabric that frays badly all call for extra. Check the number against the layout on your pattern envelope, and use the Fabric Yardage Calculator for panels and the Hem Allowance Calculator for the hem.
Choosing the fullness
A full circle has the most swing and the longest hem, which needs the most fabric. A half circle is a popular middle choice, and a quarter circle is a flared A-line shape. For the opposite approach, a gathered skirt, see the Gathering Fabric Fullness Calculator.
More shape and maker tools
For other patterns and shapes, try the Circle From Three Points Calculator, Polygon Area Calculator and Longest Length Around a Corner Calculator.
Assumptions and limits
- The waist edge is a smooth circular arc and the skirt hangs from the waist seam.
- Lengths are in inches and fabric in yards.
- The layout is a single layer of quarter circle pieces with one seam allowance on the straight edges.
- Fabric stretch, nap, pattern matching and the waistband are not included.
Frequently asked questions
How do I find the waist radius of a circle skirt?
Divide the waist measurement by 2 times pi times the fraction of a circle you are using. A 28 inch waist in a full circle gives 4.456 inches.
How much fabric does a circle skirt need?
It depends on the length and the fabric width. The example 22 inch full circle on 45 inch fabric needs 3.125 yards in a single layer layout, and a pattern with folds may need less.
Why is the hem edge longer than the waist?
The skirt flares out, so the outer circle has a bigger radius and a longer arc. The hem of the full circle example is about 166 inches around.
Should I add ease at the waist?
Add ease only if the waistband is meant to fit loosely, since the waist seam is usually attached to a band that holds the measurement. The ease option adds to the waist before the radius is worked out.