A-Line Skirt Calculator

Flare set by the seam, not a radius

An A-line skirt is a straight skirt whose side seams angle outward. The flare is defined by how much each panel edge widens, so the hem sweep is the waist plus the flare multiplied by the number of panel edges.

That makes it fundamentally different from a circle skirt, which is drafted from a radius so the fabric falls in even folds all the way round. An A-line hangs from its seams; a circle skirt hangs from its geometry.

The flare angle follows from the flare and the length: the same three inches of flare is a gentle taper on a maxi skirt and a pronounced one on a mini.

A worked example

A 28 inch waist with four panel edges flaring three inches each gives a 40 inch hem sweep — twelve inches more than the waist, over a 22 inch length, which is about a four degree side seam angle.

Double the flare to six inches per edge and the sweep is 52 inches. At that point the skirt is closer to a quarter circle in behaviour and wants the fabric to match, at which point drafting it as a circle skirt gives a better hang for the same yardage.

Where the answer misleads

Where the flare starts matters as much as how much there is. Flaring from the waist adds width exactly where the body is already widening, making the skirt stand away from the hip; starting the flare below the hip line keeps the fit clean and puts the volume where it was wanted.

The hem of a flared skirt also needs levelling after hanging, because the side seams fall partly on the bias and drop over the first day or two. Hemming immediately gives a skirt that is uneven a week later.

Finally, hem sweep is a measurement, not a look. The same 40 inch sweep reads completely differently in stiff cotton, which holds the A shape, and in drapey viscose, which falls close to the body regardless.