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Crochet hat size calculator

Size a top-down crochet hat from a head measurement: finished size, crown diameter, stitches, and every round including a partial last increase round.

Built by Monhar Wesvak

Crochet beanies in green, mustard and cream with folded brims and a faux-fur pompom
Units
Stitch terms
Measure around the forehead and above the ears.

Your result

Exact maths

Fill in the fields above to see your result.

Exact arithmetic from the numbers you entered. Your tension, yarn and blocking still decide the real fabric.

A top-down hat is a flat circle for the crown, then straight rounds down to the brim. This calculator turns a head measurement and fit into the finished hat size, the crown diameter to stop increasing at, every increase round written out, and how many rounds to work even down to the brim.

How to use the calculator

  1. Measure around the head, across the forehead and above the ears.
  2. Choose the fit: snug, standard, relaxed or slouchy.
  3. Enter the hat height from the crown to the brim.
  4. Choose the stitch and enter your stitch and round gauge.

How the calculator works

Finished circumference = head − ease

The ease is 2 in (5 cm) smaller for a snug fit, 1 in (2.5 cm) smaller for standard, the same for relaxed and 2 in (5 cm) larger for slouchy. A little negative ease keeps a beanie on the head.

The crown is a flat circle, so crown diameter = circumference ÷ π.

Stitches around = circumference × stitch gauge

Full increase rounds add 6 stitches (sc), 8 (hdc) or 12 (dc). If the target falls between two full rounds, the last round adds only the stitches still needed, spread evenly. The rest of the height is worked even:

Rounds even = height × round gauge − crown rounds

Reading your results

  • Finished hat circumference and crown diameter: stop increasing when the flat crown measures this.
  • Stitches around: with how many full and partial increase rounds make it.
  • Rounds even to the brim.
  • Round by round: every crown round written out, then the even rounds.
  • Crown options: stopping at the last full round, the partial round or the next full round, with the circumference each gives.

Worked example

A 22 in head with a standard fit makes a 21 in hat, with a crown 21 ÷ π = 6.68 in across. In single crochet at 14 stitches and 16 rounds per 4 in:

  • Stitches: 21 × 3.5 = 73.5, so 74.
  • Crown: 12 full rounds give 72 stitches; round 13 adds 2 for 74 (*35 sc, 2 sc in next st* rep twice), 21.14 in around.
  • Height: an 8 in hat is 8 × 4 = 32 rounds, so rounds 14 to 32 (19 rounds) are worked even.

US and UK terms

US sc = UK dc (6 a round), US hdc = UK htr (8), US dc = UK tr (12). Switch the terms toggle for UK instructions.

Accuracy and limits

  • The counts are exact and covered by our automated tests. The fit depends on your fabric's stretch: very stretchy stitches may need more negative ease.
  • The hat height includes the crown.
  • In metric, the ease is converted exactly from inches (2.54 cm for 1 in), so it may differ slightly from the rounded labels.
  • Children's heads vary widely: measure the wearer rather than using an age chart.

Common mistakes

  1. Measuring too high or too low. Measure across the forehead and above the ears, where the brim will sit.
  2. Measuring the crown curved. Lay it flat to compare with the crown diameter.
  3. Changing hook for the brim. A smaller hook for a ribbed brim changes the gauge; work the brim to the same circumference, or plan it separately.

Tips for more accurate results

  • Measure the crown flat as you go and stop increasing when it reaches the crown diameter, even if your round count differs a little.
  • For a folded brim or a slouchy hat, add the extra to the height you enter.
  • The double crochet bucket hat uses this method.

Frequently asked questions

How do I work out the crown diameter?

Divide the finished hat circumference by π (3.14). A 21 in hat needs a crown about 6.68 in across.

How much negative ease should a hat have?

As a guide, about 1 in (2.5 cm) for a standard beanie and 2 in (5 cm) for a snug one. Slouchy hats are made larger instead.

How much height do I add for a folded brim?

Add the depth of the fold, so a 2 in fold adds 2 in to the height you enter.

Why is my hat too wide when the crown measured right?

Your stitch gauge on the sides may differ from the crown, or the fabric stretches more than you expect. Check your stitch count against the calculator, and try a smaller hook for the sides.

Which stitch is easiest for a first hat?

Half double or double crochet works up quickly; single crochet makes a denser, warmer hat. The calculator handles all three.

Related guides and tools

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