On this page
Step 1
The basic idea
The circumference of any circle is C = 2πr. A full circle skirt forms a fabric ring whose inner opening stitches to your waistband, so that inner circle radius is r = L ÷ 2π, where L is the stitched waist opening. Every other skirt measurement builds outward from this radius.
pull-on elastic: L = max(H, W) + 5 cm (2")
Why the side seam allowance is not added to the waist
Here, W is your waist and H is your hip. For a zipper or button closure the stitched waist opening is simply your waist; the waistband controls the fit. The side seam allowance SAside is not added to the waist — it is added by moving each straight edge of the panel outward, so after the side or centre-back seam is sewn the waist is exactly W. The calculator also includes an optional advanced "waist ease" field; it defaults to 0, and anything you enter is added to L.
Step 2
Waist radius for each skirt type
A 3/4, half, or quarter circle skirt uses only a portion of the ring. Because your full waist measurement must fit along a shorter arc of the circle, the inner waist radius must become larger.
| Skirt | Fraction k | Waist radius | 28" waist (L = 28") | 71 cm waist (L = 71 cm) |
|---|---|---|---|---|
| Full circle | 1 | L ÷ 2π | 4.456" | 11.30 cm |
| 3/4 circle | 0.75 | L ÷ 1.5π | 5.942" | 15.07 cm |
| Half circle | 0.5 | L ÷ π | 8.913" | 22.60 cm |
| Quarter circle | 0.25 | L ÷ (π/2) | 17.825" | 45.20 cm |
Step 3
Subtract the seam allowance — the step most patterns skip
The radius calculated above marks the stitching line. To provide fabric for your seam allowance, you must cut inside that line: cut waist radius = r − seam allowance.
28" full circle, 5/8" SA: 4.456 − 0.625 = 3.831" ≈ 3 7/8"
What happens if you cut on the stitching line
If you cut on the stitching line and then sew a 5/8" seam, the finished waist expands by 2π × 5/8" ≈ 3.9" on a full circle — leaving a waistband that slides off your hips.
Step 4
The hem radius
Measure the skirt length from the stitching line outward, then add the hem allowance:
28" waist, 22" length, 1" hem: 4.456 + 22 + 1 = 27.456" ≈ 27 1/2"
Hem circumference (for trim and bias tape)
The finished hem circumference is 2πk × (r + length). For the example above, that equals about 166", which is essential when calculating yardage with our bias tape calculator or purchasing lace trim.
Step 5
Elastic waists need a bigger opening
A pull-on elastic skirt must stretch comfortably over your hips. Set waist opening L to the larger of hip or waist, plus 2" (5 cm) of pass-through ease (anything from 1" to 4" works).
Cut the elastic to waist − 2" (5 cm), plus 1" (2.5 cm) overlap to join the ends. Then check that the joined elastic (waist − 2") can stretch over your hips: it must reach your hip measurement at the stretch your elastic allows (about 50% for most braided and knitted waistband elastic).
elastic: 28 − 2 + 1 = 27" cut → 26" loop × 1.5 = 39" ≥ 38" hip ✓
80 cm waist, 90 cm hip: L = 90 + 5 = 95 cm; elastic 77.5 cm
If the check fails, choose a stretchier elastic or cut it longer. Either way, loop the elastic around your waist and try it on before you sew.
Step 6
From radius to yardage
When planning how much fabric for a circle skirt you need, a single full circle requires a square of side 2 × cut hem radius — 55" in this example, wider than standard 45" fabric.
Cutting the skirt into panels lets them nest efficiently. Four quarter panels on 60" fabric fit in about 51" of length (with a waistband), while eight panels on 45" fabric take about 81".
How the calculator picks a layout
The circle skirt calculator tests every panel count and every grain-safe orientation (centre line or a straight seam along or across the grain) to find the shortest layout.
Worked example
Worked metric example
For a 70 cm waist full circle skirt with a zipper, 1.5 cm seam allowances, 55 cm length, and 2.5 cm hem:
r = 70 ÷ 2π = 11.14 cm
cut waist = 11.14 − 1.5 = 9.64 cm
cut hem = 11.14 + 55 + 2.5 = 68.64 cm
The 1.5 cm side seam allowance is added along the straight edges of each panel.
Cheat sheet
Quick reference
L = W + ease for a zipper (ease default 0). Divide the waist opening by the number for your skirt type.
Full circle
r = L ÷ 6.283
28″ → 4.456″
71 cm → 11.30 cm
3/4 circle
r = L ÷ 4.712
28″ → 5.942″
71 cm → 15.07 cm
Quarter circle
r = L ÷ 1.571
28″ → 17.825″
71 cm → 45.20 cm
