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The Yarn Math › Hat size

Hat Size Calculator

Pick a size or enter a head measurement, add your gauge, and get the cast-on, the finished size and when to start the crown. For knitting and crochet.

Your hat

    Sizes and heights are typical values from the Craft Yarn Council and Knit Picks charts. Measuring the actual head is always better.

    How many stitches do I cast on for a hat?

    Measure the head, take off 5–10% so the hat stays on, then multiply by your stitches per inch. For an adult woman (22 in head) at 20 stitches per 4 inches, that is about 96 stitches.

    What is negative ease?

    Making the hat a little smaller than the head. Ribbed knitted hats usually have about 10% negative ease; crochet is less stretchy, so 0–5% is common.

    How tall should a beanie be?

    For an adult, around 8–9 in for a fitted beanie without a folded brim, about 11 in with a fold-up brim, and 11–12 in or more for a slouchy hat.

    Why is the stitch count a multiple of 8?

    A classic crown decreases 8 stitches every other round, and most ribbing works over 2 or 4 stitches, so a multiple of 8 fits both. You can change the multiple.

    Hat size chart by age → · How much yarn for a hat

    How the calculator works

    For knitting, it takes the head circumference, removes the ease for the fit you chose, and multiplies by your stitch gauge. The result is rounded to your stitch multiple. It then works out how long a classic 8-point crown takes at your row gauge, so you know when to start decreasing.

    For crochet worked from the top down, the crown is a flat circle. Its diameter is the finished circumference divided by π (about 3.14), so you increase until the circle measures that much across, then work even to the hat height.