Circle skirt calculator
Enter your waist and the finished length. Works in centimetres or inches, and tells you whether the pieces will fit your fabric width.
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How do you calculate the radius for a circle skirt?
Divide the waist measurement by 2π for a full circle skirt — a 70 cm waist gives an 11.14 cm radius. For less than a full circle, divide by the fraction as well: a half circle skirt needs double the radius, 22.28 cm for the same waist. Then subtract your seam allowance, because the allowance is turned under into the waistband and the hole you cut must be that much smaller.
Why a half circle skirt needs a bigger hole, not a smaller one
This is the step that trips people up, and it is worth understanding rather than memorising. The waist opening is an arc, and its length has to equal your waist. In a full circle skirt that arc goes all the way round, so a small radius produces enough length. In a half circle skirt only half the circle is there, so the same waist measurement has to come out of half as much arc — which means twice the radius.
Quarter circle, four times the radius. It feels backwards the first time, but the arithmetic is unavoidable.
Cutting a half circle skirt using the full circle radius is the single most common circle skirt mistake, and it produces a waist that will not go over the hips.
Seam allowance comes off the radius, not added to it
The waistline seam allowance sits inside the circle. It gets turned under and joined to the waistband, disappearing from the finished garment.
So the hole you cut has to be smaller than the finished waist radius by exactly that allowance. Adding it instead — the instinct, since you add allowance everywhere else — gives a waist two allowances too big, which on a 1.5 cm allowance is a full 9.4 cm of extra waist circumference.
At the hem the opposite applies: the hem allowance is added to the outer radius, because it is turned under below the finished length.
Fabric width usually decides the layout, not the yardage
A full circle skirt for an average waist and a knee length needs a circle roughly 130 cm across. Standard quilting cotton is 110 cm wide. The circle simply will not fit, so it gets cut as four quarter panels with seams — which is why so many circle skirt patterns have side seams that seem unnecessary.
Wider fabric changes the whole calculation. At 150 cm you may fit two panels side by side; on 280 cm wide fabric a whole circle can often be cut in one piece with no seams at all.
Enter your fabric width and the calculator works out how many panels fit across, how many rows you need, and the total length to buy.
Bias stretch and why you hem a circle skirt last
A circle skirt hem crosses every grain direction. Where the hem runs on the true bias — at roughly 45° to the weave — the fabric will stretch and hang lower over time. Where it runs on the straight grain it will not move.
This is why the hem on a finished circle skirt is never level if you hem it flat on the table. The standard remedy is to hang the finished skirt for at least 24 hours, ideally longer for heavier fabric and for anything cut on a loose weave, then trim the hem level while it is on the body or a form.
Allow a little extra length for that trimming. It is easier to cut a hem shorter than to find fabric to lengthen it.
The formula
Everything comes from the waist arc and the fraction of a circle you are cutting.
waist arc = waist measurement + easewaist radius = arc ÷ (2π × f)f = 1 full circle · 0.75 three-quarter · 0.5 half · 0.25 quarterradius to cut = waist radius − seam allowanceouter radius = waist radius + finished length + hem allowancehem circumference = 2π × (waist radius + length) × ffabric needed: a single circle fits if fabric width ≥ 2 × outer radiusotherwise cut ⌈4f⌉ panels and stack them by rows
The ease figure is a matter of taste and of what the skirt fastens with. A skirt with a zip needs very little — 1 to 2 cm is typical. A pull-on elastic waist has to pass over the hips, so it either needs enough ease to do that or an elastic waistband that stretches. Check the hip measurement before committing to a pull-on style.
Note that f appears in the denominator. That is the whole reason a smaller fraction of a circle needs a larger radius: less arc is available, so the radius must grow to produce the same waist length.
Worked example: a knee-length full circle skirt
A 70 cm waist, 2 cm ease, 55 cm finished length, 1.5 cm seam allowance, 2 cm hem, on 150 cm wide fabric.
- Waist arc = 70 + 272 cm
- Waist radius = 72 ÷ (2π × 1)11.46 cm
- Radius to cut = 11.46 − 1.59.96 cm
- Outer radius = 11.46 + 55 + 268.46 cm
- Full circle needs a width of 2 × 68.46136.9 cm
- Fits in 150 cm — cut as one piece136.9 cm of fabric
Cut a 9.96 cm radius hole, an outer radius of 68.46 cm, from about 1.4 m of 150 cm fabric.
On 110 cm quilting cotton the same skirt will not fit as one circle. It would be cut as four quarter panels, one per row, needing about 2.74 m — twice the fabric for the same garment.
Choosing the fullness
- Full circle — the deepest, most even drape and the most dramatic twirl; uses the most fabric
- Three-quarter — nearly the full effect with noticeably less fabric; a good compromise
- Half circle — folds fall more to the sides than the front; much easier to fit on narrow fabric
- Quarter circle — closest to an A-line; least fabric, least movement, most forgiving layout
Terms on this page
- Ease
- Extra measurement added beyond the body measurement so the garment is wearable. A zipped waistband needs 1–2 cm; a pull-on style needs enough to clear the hips or an elastic waistband.
- True bias
- The 45° direction across a woven fabric, where it stretches most. A circle skirt hem crosses the bias four times, which is why it drops unevenly.
- Seam allowance
- The margin between the cutting line and the stitching line. At the waist it is subtracted from the radius; at the hem it is added to it.
- Hanging the hem
- Leaving a finished skirt suspended for a day or more so the bias sections drop, then trimming the hem level. Skipping this leaves a hem that goes crooked after the first wear.
Common questions
What is the radius formula for a circle skirt?
Waist measurement plus ease, divided by 2π times the fraction of a circle. A full circle uses f = 1, a half circle f = 0.5, a quarter f = 0.25. Then subtract your seam allowance to get the radius you actually cut.
Why does a half circle skirt need a larger radius than a full circle?
Because the waist opening is an arc, and a half circle only has half as much arc available. To produce the same waist length from half the arc, the radius has to double. Quarter circle skirts need four times the full circle radius.
Do I add or subtract the seam allowance at the waist?
Subtract it. The allowance is turned under into the waistband seam and disappears from the finished garment, so the hole you cut must be smaller than the finished waist radius by exactly that amount.
How much fabric does a circle skirt need?
It depends far more on fabric width than on the skirt. A knee-length full circle skirt fits as one piece on 150 cm fabric using about 1.4 m, but needs roughly 2.7 m of 110 cm fabric cut as four panels. Enter your width above to get the figure for your own measurements.
Why is my circle skirt hem uneven?
Because the hem crosses the bias, where woven fabric stretches, and the bias sections drop over time while the straight-grain sections do not. Hang the finished skirt for at least 24 hours, then trim the hem level before finishing it.
Where these numbers come from
- Wolfram MathWorld — Circular sector The arc length relationship the radius formula is derived from.
- Government of Canada — Textile labelling and advertising regulations Governs how fabric width and fibre content must be declared on textiles sold in Canada.
Last verified 2026-08-01 The method on this page is checked against the sources above at least once a year. Spotted something out of date? Tell us and we will fix it.
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