Circle Skirt Calculator
A circle skirt is one measurement away from a pattern. Enter your waist, the fullness you want, and the finished length to get the waist radius to mark, the outer radius to cut, and the fabric it needs.
Circle skirt hems are curved and usually narrow — half an inch to an inch is typical.
Formula & how it works
The waist opening is an arc of a circle. For a fraction f of a full circle, radius = waist ÷ (2π × f) — so f is 1 for full, 0.5 for half, and 0.25 for quarter.
Outer radius is waist radius + length + hem. A full circle needs a square of 2 × outer radius, a half circle needs 2 × outer by outer, and a quarter needs outer × outer.
Worked example
A 28 inch waist with half an inch of ease gives a full-circle waist radius of about 4.54 inches. Adding a 24 inch length and 1 inch hem makes the outer radius 29.54 inches, so the skirt needs roughly a 59 inch square. As a half circle the waist radius grows to 9.08 inches but the fabric drops to about 60 by 30 inches.
Cutting a circle skirt
Why the radius changes with fullness
The same waist has to fit around a shorter arc as you move from full to half to quarter circle, so the radius must grow to compensate. That is why a quarter circle skirt has a surprisingly large waist curve — it is a small slice of a much bigger circle.
Fabric width is the real constraint
A full circle skirt of any real length rarely fits within a single fabric width, which is why they are usually cut in two halves with side seams, or in four quarters. Checking the outer radius against your fabric width before buying tells you how many lengths you actually need.
Let it hang before hemming
Parts of a circle skirt hem sit on the straight grain and parts on the bias, and bias stretches under its own weight. Hanging the finished skirt for a day or two lets that happen before you level and cut the hem, which is the difference between an even hem and a wavy one.