Circle Skirt Calculator
A circle skirt is one piece of fabric with a hole in the middle, and the hole has to be exactly as long around as the waist it hangs from, so its radius is the waist measurement divided by 2 pi. This calculator does that division on the first screen and then shows the rest of the pattern beside it: a 28 in waist on a full circle gives a 4.46 in waist radius, a 28.46 in hem radius on a 24 in skirt, a 56.91 in square to cut from, and 1.6 yd of 60 in goods. What it does differently is keep the allowances honest and the fullness in view. The seam allowance moves the cutting circle inward by exactly its own width and is never added at the hem as well, ease is added to the waist once before the division, and the same numbers are answered at all three fullnesses at once, so you can see that the half circle wants 8.91 in at the waist and the quarter circle 17.83 in before you cut anything. Work in inches with fractions such as 28 1/2 and 5/8, or switch to centimetres and the numbers convert with you: a 60 cm waist comes out at 9.55 cm. The formula is exact, while calculated radii are bounded approximations. Fabric figures use simple sequential bounding rectangles and exclude joining seam allowances, openings, waistband, matching, nap and shrinkage; they are not complete garment patterns. Inch/cm suffixes retain physical meaning, and switching units now preserves every supplied measurement, including 60 in goods as 152.4 cm. Tiny positive values and shortened displays are marked, and the complete report retains the supplied values, exact formula and calculation bounds.
fullness full circle waist + ease 28 in length 24 in waist radius ≈ 4.46 in waist cut ≈ 4.46 in hem radius ≈ 28.46 in hem cut ≈ 28.46 in cut rectangle ≈ 56.91 x ≈ 56.91 in fabric estimate 1.6 yd Joining seam allowances excluded. Complete formula, bounds and assumptions below.
Waist radius = (supplied waist + ease) ÷ (2π × circle fraction). A half circle has twice the full-circle waist radius; a quarter has four times it. The waist seam allowance moves its cut circle inward once, and the hem allowance moves the outer edge outward once. Fabric quantity depends on goods width and the rectangle model; less fullness does not always use less fabric.
Inch/cm suffixes carry their stated unit. Unit changes preserve every supplied physical measurement, including goods width: 60 in converts to 152.4 cm. Fractions, mixed numbers, scientific notation and commas grouping thousands are accepted. Use a full stop for decimals.
Radii are approximations; ordinary displays round to two decimals and tiny positive values are marked. The complete report gives the exact formula and strict calculation bounds. The fabric estimate rounds the upper calculated length upward to a tenth of a yard or metre. Numbers accept up to 8192 characters, 512 significant digits per component and normalized decimal scales from -4096 to 4096. No garment-size cap is imposed.
One simple bounding rectangle fits the supplied usable width. This is an arithmetic fabric estimate, not a printable pattern or grain, opening or garment-fit instruction.
The same waist, three fullnesses
Each row uses the same supplied measurements. Its copy includes its own complete report and assumptions. Joining seam allowances are excluded from every fabric estimate.
Complete selectable report
Common questions
- How do I calculate the waist radius for a circle skirt?
- Divide the waist measurement by 2 pi, which is about 6.2832, and for a full circle that is the radius of the hole you cut. A 28 in waist gives 4.46 in, and a 60 cm waist gives 9.55 cm. Less fullness means the same waist is spread over less of a circle, so the division changes with it: divide by 2 pi times 0.5 for a half circle and by 2 pi times 0.25 for a quarter. The outer radius is that waist radius plus the finished length, so a 24 in full circle skirt is marked at 4.46 in and again at 28.46 in from the same centre point.
- What is the difference between a full, half and quarter circle skirt?
- The fullness is how much of a circle the waist opening is cut from, and it decides both the sweep of the hem and the size of the hole. On a 28 in waist the full circle waist radius is 4.46 in, the half circle is 8.91 in and the quarter circle is 17.83 in: less fullness means a bigger hole and a straighter, narrower skirt. Fabric does not always follow that order, and the calculator shows it rather than hiding it. On 60 in goods with a 24 in length the full circle fits in one piece at 1.6 yd, while the half circle has a 65.83 in straight edge that will not cross 60 in goods, so it is cut as two panels at 1.9 yd; the quarter circle takes 1.2 yd. The three rows under the readout answer all three at once.
- Do I add the seam allowance to the waist radius or take it away?
- Take it away. The waist radius is the finished measurement, so the allowance sits inside it: cut the circle smaller by the allowance and the seam falls back on the line you calculated. With a 4.46 in waist radius and a 5/8 in allowance, the cutting circle is 3.83 in. This tool keeps that separate from the finished figure, shows both, and never adds the waist allowance at the hem as well, which is the double count that makes a finished waist come out too big. A hem allowance works the other way and is added outside the finished edge.
- How much fabric does a circle skirt need?
- It depends on the outer radius and the usable width of your goods, so enter the width and the estimate follows the layout. A full circle whose diameter fits across the fabric is cut in one piece from a square, which is 1.6 yd for the 28 in, 24 in example on 60 in goods. When the full circle is wider than the fabric, it is cut as four quarter panels joined by four seams, and the same skirt takes 3.2 yd of 45 in goods. Pieces are laid with the straight grain running down the skirt rather than turned sideways, the figure is rounded up to the nearest tenth of a yard or metre, and goods narrower than one cut radius are reported as too narrow instead of guessed at. These are geometric rectangle estimates, not complete panel cutting layouts: joining seam allowances and garment openings are excluded. Goods width is the usable width supplied, and each unit change preserves that physical width.
- Should I add ease to the waist measurement?
- That is your call, and the ease field is there for it: whatever you enter is added to the waist once, before the division, so 28 in with 1 in of ease is worked as 29 in. Because the division is by 2 pi, an inch of ease only moves the radius by about 0.16 in, which is why measuring the waist carefully matters more than the ease does. Leave the field empty and no ease is added at all.
- Can I work in centimetres, or type fractions of an inch?
- Both. Fractions read the way you write them on a pattern: 28 1/2, 28-1/2 and 5/8 are accepted, as are decimals, scientific notation and commas grouping thousands. An inch or cm suffix carries its stated physical unit even when the form displays the other unit. Switching units converts every supplied measurement exactly: 28 in becomes 71.12 cm and 60 in goods become 152.4 cm. Invalid or incomplete drafts stay on screen unchanged. Radii use the exact symbolic formula with bounded approximations, and the ordinary readout rounds to two decimals; the full report includes the formula and strict bounds.
- Does anything I type here leave my browser?
- The measurements and reports stay in this browser; there is no account or upload. Restoration does not rewrite saved records, and only valid deliberate changes save. Invalid drafts stay on screen. Unknown, unedited, incompatible or concurrently changed saved values are preserved; Forget saved settings removes the stored record and leaves the current calculation. If storage is blocked, calculation and copying still work. Privacy-aware completion and copy events use static metadata and never send measurements or reports.
Exact geometry: the waist radius is the circumference divided by 2π, adjusted for the fullness you choose. Seam allowance and hem allowance are added only if you enter them.