Hat Size Calculator

How the crown shaping is figured

This treats the hat as a cylinder (the straight body) topped with a flat circle (the crown), built bottom-up. The crown's depth is estimated from its radius, so the calculator subtracts that from your total height to get how far to work straight before starting decreases. It's an approximation — heads aren't perfect cylinders — but it's a solid starting plan that you can adjust by trying the hat on as you go.

Why negative ease matters more than it seems

Crocheted fabric has far less natural stretch than knit fabric, so a hat made to your exact head circumference will usually feel loose and slip down rather than sitting snugly. A stretchier stitch (like a ribbed post-stitch pattern) can get away with less negative ease than a stiff, dense stitch worked in worsted-weight cotton, which barely stretches at all — if you're working in a non-stretchy stitch, consider using 1.5 to 2 inches of negative ease rather than the default 1 inch here.

Adjusting for a folded brim

If you plan to fold up a cuff or brim at the bottom edge, add the doubled height of that fold to your total hat height before calculating — a 2-inch folded cuff needs 4 extra inches of fabric, not 2, since it folds back on itself. Skipping this is a common reason a finished hat ends up shorter than expected once the brim is folded into place.

The decrease plan here uses a standard spiral or joined-round crown, decreasing evenly around each round. Some patterns instead cluster all the decreases for a round into one section (a "pie slice" crown) — both approaches use the same total stitch count, but a pie-slice crown can pull slightly off-center if your tension varies through the round, so an evenly distributed decrease is usually the safer default for a first attempt at a size.