How much fabric do you need for a circle skirt?

A circle skirt is honest geometry: one waist hole, one big circle of fabric. That makes it the rare garment where you can compute the yardage yourself instead of trusting a chart. It also hides a trap: a few centimetres of extra length can triple the fabric you need.

The formula

A full circle skirt is a ring. The inner radius comes from your waist, the outer radius adds the skirt length:

waist radius  r = waist circumference / (2 × π)
outer radius  R = r + skirt length + hem allowance

For a 72 cm waist, r is about 11.5 cm. With 45 cm of length and a 2 cm hem, R is about 58.5 cm. Cut as a single piece, the circle needs a square of fabric 2R on each side. So the amount of fabric to buy is simply 2R, provided 2R fits inside the fabric width. Add your waistband and seam allowances on top; your pattern defines those.

The table, and the cliff inside it

Same waist (72 cm), 2 cm hem, fabric 140 cm wide. Watch what happens between 55 and 60 cm:

The 55 cm row deserves a warning: 137 cm of circle on 140 cm of fabric leaves 3 cm total, before any shrinkage and before the selvedges come off. On 150 cm fabric the same skirt is comfortable. This is why two people with "the same skirt" report needing wildly different yardage: they had different fabric widths.

Past the cliff, you cut two half circles and sew side seams (or a centre back seam plus one side). Each half circle is a piece 2R wide and R tall. Once 2R exceeds the fabric width, the pieces have to lie lengthwise, one after the other, and you pay about 2 × 2R of fabric. Cutting four quarter panels instead can claw some of that back, because quarter circles interlock when you rotate them. Whether they may rotate depends on your fabric, which brings us to the next point.

One-way fabric changes the answer

Velvet, corduroy, panne and any print with an obvious up and down are one-way: every piece must point the same direction. That forbids exactly the head-to-tail tricks that save fabric on long skirts. A rotatable quarter-panel layout that squeezes into 2.4 m can need a full 3 m once the pieces must all face up. If you are buying a directional fabric, compute the one-way case, not the best case.

Half circle skirts are friendlier

A half circle skirt takes the same waist but only half the sweep. The waist radius doubles (r = waist / π), the outer circle shrinks, and the pieces pack much better: a 60 cm half circle skirt fits in roughly 1.7 m of 140 cm fabric instead of 3 m. If the cliff just ate your budget, this is the classic way around it.

Getting the exact number instead of "about"

Everything above assumes a perfect circle and a 72 cm waist. Your pattern is not that: your waist differs, your pattern adds seam allowances, maybe a waistband, maybe pockets, and your fabric has its own width. The honest way to the exact number is to lay the real pieces onto the real width and measure. You can do that on the floor with tape, or you can let software do it.