Half circle (180°)
Soft flare that swishes when you walk.
- Waist radius
- L ÷ π = 9 1⁄2"
- Cut hem radius
- 34 1⁄2"
- Hem circumference
- 105 3⁄8"
- Fabric to buy
- 1 1/4 yd (1.1 m) · 2 panels
Free calculator · half & quarter circle
Half Circle Skirt Calculator & Quarter Circle Pattern
A half circle gives gentle flare with far less fabric than a full circle; a quarter circle makes a clean A-line. Enter your waist and length for exact radii, yardage and a 1:1 pattern.
- Half, quarter, ¾ & full
- 45" / 60" layout planner
- Tiled 1:1 PDF pattern
Cut waist radius
8 1⁄4"
21.1 cm · radius − seam allowance
Cut hem radius
31 7⁄8"
81.1 cm · radius + length + hem
Waist radius (stitching)
8 7⁄8"
22.6 cm
Fabric to buy
1 1/8 yd
1.0 m · 2 panels
Hem circumference
97 1⁄8"
246.7 cm
Waist opening sewn
28"
71.1 cm · waist (side SA is on the straight edges)
Waistband piece
30 1⁄2" × 4 1⁄4"
waist + 2 SA + overlap
Leave a zipper opening long enough that waist opening + zipper length clears your hip (40"); a 7–9" (18–23 cm) zipper usually does.
Pattern piece
Cut waistStitching linesCut hem
Fabric layout on 60" fabric
2 panels of 90° on open fabric, using 36 3⁄4" (93.4 cm) of length, waistband included. Selvedges run along the top and bottom.
Grain: panels are never turned to odd angles - one straight seam edge of every panel runs along the lengthwise grain, parallel to the selvedge (marked as the green line on the layout; the arrow shows the selvedge direction). The hem still crosses the bias, which is normal for a circle skirt.
How the 1:1 pattern works:
- The printed pattern is ONE quarter-circle template (90 deg) at 1:1. Tape the pages together into that quarter, then use it x2 in total for this skirt (2 quarters = 180 deg).
- Your layout has 2 quarter panels: cut the template 2 times, following the dotted lines on both straight edges (seam allowance included).
- Free, no sign-up
- Runs in your browser — nothing uploaded
- True-scale 1:1 PDF with test squares
- Inches & centimeters
Half vs quarter
Half circle or quarter circle?
Same waist, same length, very different skirts. Both cards use a 30" waist, 24" length and 60" fabric.
Quarter circle (90°)
Slim A-line with little volume.
- Waist radius
- L ÷ (π/2) = 19 1⁄8"
- Cut hem radius
- 44 1⁄8"
- Hem circumference
- 67 3⁄4"
- Fabric to buy
- 1 yd (0.9 m) · 2 panels
How it works
Half circle skirt in four steps
Step 1: Measure
Measure your waist where the skirt will sit, and your hip if you want a pull-on elastic waist. Decide the finished length.
Step 2: Pick shape & fabric
Choose Half or Quarter and your fabric width. The planner compares one piece with two or four panels and keeps the shortest.
Step 3: Print the pattern
Download the tiled 1:1 PDF, print at 100%, check the test squares and tape the pages together.
Step 4: Cut & sew
Cut along the red lines, sew the seam, add the waistband and let the skirt hang overnight before hemming.
Worked examples
Two skirts, real calculator output
Open either example to load the same numbers into the calculator and change what differs for you.
Worked example
Knee-length half circle with a zipper
- Waist
- 30"
- Length
- 24"
- Fabric width
- 60"
- Seam / hem
- 5/8" / 1"
Result
- Cut waist radius
- 8 7⁄8"
- Cut hem radius
- 34 1⁄2"
- Fabric to buy
- 1 1/4 yd (1.1 m)
- Layout
- 2 panels, waistband included
Worked example
Pull-on elastic quarter circle
- Waist / hip
- 28" / 38"
- Length
- 22"
- Fabric width
- 60"
- Elastic stretch
- 50%
Result
- Waist opening
- 40" (hip + 2")
- Cut waist radius
- 24 7⁄8"
- Elastic to cut
- 27"
- Fabric to buy
- 1 1/8 yd (1.1 m)
A quarter circle has the smallest waist curve, so with elastic the opening is sized from the hip — otherwise it would not pull on.
The math
Half circle skirt formula
L = waist + ease (zipper, ease default 0) or max(hip, waist) + 5 cm (elastic)
r = L ÷ π (half) r = 2 × L ÷ π (quarter)
cut waist = r − seam allowance cut hem = r + length + hem allowance
r = L ÷ π (half) r = 2 × L ÷ π (quarter)
cut waist = r − seam allowance cut hem = r + length + hem allowance
The waist curve of a half circle is half a circumference, so the radius is the waist opening divided by π. A quarter circle is half that curve again, so its radius doubles.
Show the 30" waist example step by step
L = 30", so r = 30 ÷ π = 9.549". With a 5/8" waist seam allowance you cut the waist at 8.924" ≈ 8 7⁄8". A 24" skirt with a 1" hem is cut at 9.549 + 24 + 1 = 34.549" ≈ 34 1⁄2". Side seam allowance is added outside the straight edges, not to the waist.
Derivations for every style are in the circle skirt math formula guide.
Fabric layout
Laying out on 45" and 60" fabric
Diagrams drawn by the calculator for the 30" × 24" half circle.
60" / 150 cm fabric
Wide fabric: 1 1/4 yd
On 60" fabric the planner uses 2 panels and 42" of length, waistband included. Wider bolts let the half circle nest with the least waste.
45" / 115 cm fabric
Narrow fabric: 1 3/4 yd
On 45" fabric the cut hem radius (34 1⁄2") no longer fits across, so the skirt splits into 2 panels with a centre back seam and uses 59".
How panels stay on grain
The planner only turns panels so a straight seam or the centre line stays on the grain, and the diagram draws that grain arrow. The hem still crosses the bias, which is why you let the skirt hang before hemming.
Tips
Tips for half and quarter circle skirts
Zip at centre back
A centre back seam is the natural, clean place for an invisible zipper.
Watch directional prints
Panels turned 180° put the print upside down on half the skirt — choose one piece or set panels manually.
Bind the curved hem
A narrow hem or binding follows the curve best; the bias tape calculator sizes the square.
Want more twirl?
Switch to the full circle in the circle skirt calculator — about 1 1/2 yd vs 1 1/8 yd for a 28" × 22" skirt.
Frequently asked questions
How do you calculate a half circle skirt?
Take your waist (plus any optional ease) as the waist opening and divide by π to find the waist radius; side seam allowance is added to the straight edges, not the waist. Subtract the waist seam allowance for the cutting line, and add your skirt length plus hem allowance for the cut hem radius.
How much fabric does a half circle skirt need?
About half the yardage of a full circle. A 28" waist, 22" half circle on 60" fabric takes 1 1/8 yd in 2 panels, versus 1 1/2 yd for a full circle. Enter your measurements above for exact yardage.
Is a quarter circle skirt the same as an A-line skirt?
Close. A quarter circle skirt is a simple A-line with a smooth flare and no darts, cut as one piece with a single seam.
Where does the seam go on a half circle skirt?
Usually at centre back, where the zipper goes. Two panels put seams at both sides or at centre front and back.
Can a quarter circle skirt have an elastic waist?
Yes, but enter your hip. The quarter circle waist curve is small, so the calculator sizes the opening from max(hip, waist) + 2" pass-through ease and checks that the elastic stretches over your hip.
Why is my half circle split into two panels?
A one-piece half circle needs fabric at least as wide as the cut hem radius plus seam allowance. When that is wider than the bolt, two quarter panels nest head-to-toe and usually shorten the layout.
Guides
Half circle sewing guides
Ready to cut your half circle?
Enter your waist and length — get the radius, the 45" or 60" layout and a 1:1 PDF pattern in seconds.