Hat size calculator

How to use it

• Measure the head, or pick a size to use the middle of the Craft Yarn Council range for it.
• Enter your gauge from a washed swatch in the hat's main stitch. Round gauge is optional, but without it the calculator can't tell you when to start the crown.
• For a knitted hat, choose the rib for the brim and how many sections the crown has. The cast-on is rounded to fit the rib.

How it works

The hat is made smaller than the head by the percentage you choose, then your gauge turns that size into stitches.

hat size = head × (1 − ease ÷ 100)
stitches = hat size × gauge stitches ÷ 4, rounded to the rib
crown: decrease 1 stitch per section every other round until half are gone, then every round until 1 per section is left

Example: a 22 in head made 10% smaller gives a 19.8 in hat. At 20 stitches in 4 in that's 99 stitches, and the nearest count that fits 2×2 rib is 100, so cast on 100 for a 20 in hat. For an 8-section crown, decrease 4 stitches on the last round before the crown to make 96, which is 12 stitches per section. Decreasing every other round 6 times leaves 48 stitches, and decreasing every round 5 more times leaves 8. That's 17 rounds, which at 28 rounds in 4 in is 2.4 in. So for an 8 in hat, work until it measures 5.6 in, then start the crown.

For a crochet hat worked from the top down, the top is a flat circle. A circle's width across is its distance around divided by π (about 3.14), so a 19.8 in hat needs a circle 6.3 in across before you stop increasing.

Head sizes

Head circumference ranges from the Craft Yarn Council's head circumference chart. The ranges overlap, so measure the head when you can.

Tips

• Rib pulls in and stretches back out, which is why ribbed hats can take more negative ease than hats in stockinette or crochet.
• Make the hat a little taller, about 1 in (2.5 cm), if you want to fold the brim up.
• If the crown looks pointed, choose more sections; for a slouchy hat, choose fewer and make the body longer.
• For a crochet hat, check the stitch count at the end of your last increase round against the count shown in the result. They should be close.