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Crochet hat size calculator: crown increases and height

Pick a size or measure the head, enter your gauge, and get a round-by-round crown for a top-down hat: how many stitches to increase to, and how many plain rounds take it to the right height.

Head sizes: Craft Yarn Council chart, middle of each range.
About 2.5 cm keeps a beanie on; 0 for slouchy.

The prefilled gauge is an example for single crochet in medium (worsted) yarn. Measure your own washed swatch in the round.

Increase to 75 stitches

13 + 21

13 increase rounds, then 21 rounds without increasing: 34 rounds in all.

The hat measures about 53.6 cm around, for a 53.3 cm target.

Round by round

  1. Round 1: Work 6 sc into a magic ring. (6 stitches)
  2. Round 2: 2 sc in each stitch. (12 stitches)
  3. Round 3: [sc in the next stitch, 2 sc in the next stitch] 6 times. (18 stitches)
  4. Round 4: [sc in the next 2 stitches, 2 sc in the next stitch] 6 times. (24 stitches)
  5. Round 5: [sc in the next 3 stitches, 2 sc in the next stitch] 6 times. (30 stitches)
  6. Round 6: [sc in the next 4 stitches, 2 sc in the next stitch] 6 times. (36 stitches)
  7. Round 7: [sc in the next 5 stitches, 2 sc in the next stitch] 6 times. (42 stitches)
  8. Round 8: [sc in the next 6 stitches, 2 sc in the next stitch] 6 times. (48 stitches)
  9. Round 9: [sc in the next 7 stitches, 2 sc in the next stitch] 6 times. (54 stitches)
  10. Round 10: [sc in the next 8 stitches, 2 sc in the next stitch] 6 times. (60 stitches)
  11. Round 11: [sc in the next 9 stitches, 2 sc in the next stitch] 6 times. (66 stitches)
  12. Round 12: [sc in the next 10 stitches, 2 sc in the next stitch] 6 times. (72 stitches)
  13. Round 13: 1 sc in each stitch, increasing 3 times spaced evenly (2 sc in about every 24th stitch). (75 stitches)
  14. Rounds 14–34: 1 sc in each stitch. (75 stitches)
Working from the brim up instead

Start with 75 stitches and work 21 rounds even, then decrease in this order:

  1. 1 sc in each stitch, decreasing 3 times spaced evenly (sc2tog). (72 stitches)
  2. [sc in the next 10 stitches, sc2tog] 6 times. (66 stitches)
  3. [sc in the next 9 stitches, sc2tog] 6 times. (60 stitches)
  4. [sc in the next 8 stitches, sc2tog] 6 times. (54 stitches)
  5. [sc in the next 7 stitches, sc2tog] 6 times. (48 stitches)
  6. [sc in the next 6 stitches, sc2tog] 6 times. (42 stitches)
  7. [sc in the next 5 stitches, sc2tog] 6 times. (36 stitches)
  8. [sc in the next 4 stitches, sc2tog] 6 times. (30 stitches)
  9. [sc in the next 3 stitches, sc2tog] 6 times. (24 stitches)
  10. [sc in the next 2 stitches, sc2tog] 6 times. (18 stitches)
  11. [sc in the next stitch, sc2tog] 6 times. (12 stitches)
  12. sc2tog 6 times. (6 stitches)

Thread the tail through the last stitches and pull the crown closed.

How the plan is worked out

A flat circle stays flat when it grows by the same number of stitches every round: 6 for single crochet, 8 for half double and 12 for double crochet. The crown increases until its edge reaches the hat circumference, which is the head less the amount you made it smaller by. The last increase round spreads only the increases still needed, so the crown lands on the nearest whole stitch. After that, plain rounds take the hat to its height.

The flat crown reaches about the hat circumference ÷ 3.14 across before the sides start. If your circle ruffles or cups before then, your stitch height and the increase rate disagree: see curling, cupping and ruffling. Check the hat on the head, or around a ball the same size, before the last rounds.

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