half circle skirt calculator

How this half circle skirt calculator works

A half circle skirt is drafted from a semicircle shape, which gives you soft drape with less volume than a full circle skirt. The most important value is the waist radius, because that controls how the waist opening fits your body. This calculator uses your waist measurement (plus optional ease) to compute the sewing-line radius, then expands it for skirt length and hem allowance.

For a half circle skirt, the waist arc equals π × radius, so the core formula is: radius = waist / π. From there, we add skirt length to find the outer radius and include allowances so you can cut with confidence.

What you get from the calculator

• Waist stitching-line radius (the radius that matches your body measurement and ease).
• Waist cutting-line radius (adjusted for waist seam allowance).
• Outer stitching-line radius (waist radius + finished length).
• Outer cutting-line radius (includes hem allowance).
• Cut diameter for layout planning.
• Fabric area estimate and optional linear fabric estimate if width is provided.

Measurement tips for better fit

1) Measure the true waist point

Wrap a soft measuring tape around the exact place where you want the waistband to sit. Keep the tape level and snug, but not tight. If your skirt will sit lower than your natural waist, measure that point instead.

2) Decide on ease intentionally

If your skirt includes a zipper and fitted waistband, you may use very little ease. If it has an elastic waist or you prefer comfort, add a bit more ease. Small changes (like 1 to 2 cm or 1/4 to 3/4 in) can noticeably affect fit.

3) Don’t skip hem allowance

Circle-based hems can stretch while hanging, so extra hem allowance gives you room to true the hem before final finishing. Always let the skirt hang before hemming for the most even result.

Practical cutting notes

• Prewash fabric when needed to avoid post-sew shrinkage surprises.
• Mark grainline clearly before cutting curved edges.
• Use tailor’s chalk or washable marker for arcs and notches.
• If your fabric has directional print or nap, account for it in layout.
• Add extra fabric for matching plaid, stripe, or large motifs.

Quick FAQ

Is this for a true half circle and not a full circle?

Yes. The calculator uses the half-circle waist relationship, where waist equals π times radius.

Why can fabric estimates vary in real projects?

Real usage changes with fabric width, directional print, seam placement, panel splitting, and whether you include waistband/interfacing. Use the estimate as a guide, then add a safety margin for your chosen layout.

Can I use inches instead of centimeters?

Absolutely. Select inches in the unit dropdown and the tool handles conversion automatically while still showing both metric and imperial outputs.