The Secret Formula for Knitted Baby Hats That Fit Every Time

Whether you’re knitting hats to donate to babies in the NICU or for people you love, hats are a great, practical gift for babies and new parents. One of the trickiest parts of knitting for babies is sizing.

When I had my first baby, I had a hard time figuring out what clothes he would need in each size per season. Would a baby born in the spring need 6- or 9-month clothing in the winter?  Some babies are big and some babies are small, and baby’s heads grow the fastest in the first year.

How will you know what size will fit best?

Cabled Baby Hat Knitting pattern

To help you whip up baby hats of all sizes, here is a little chart to help you determine what size hat you’d like to make so you don’t end up making a hat too big or too small when winter rolls around.

Average Baby Head Measurments By Size

  • Preemie head size: 9-inch circumference and 4 inches tall
  • Newborn size: 11-inch circumference and 5 inches tall
  • 0-3 month size: 13-inch circumference and 6 inches tall
  • 3-6 month size: 16-inch circumference and 7 inches tall
  • 6-9 month size: 18-inch circumference and 7.5 inches tall
  • 12 month size: 20-inch circumference and 8 inches tall
  • 24-4T size: 21-inch circumference and 8.5 inches tall

Using the above sizing information, here is the formula to determine how many stitches you need to cast on in the round to knit that baby hat size:

Circumference (in inches) x stitches per inch = cast on number

If you’ve knit several baby hats before, you can use the above formula with any weight of yarn and appropriate needle size. Knit until you get half an inch shorter than the desired hat. Bind off by k2tog every five stitches until you have one stitch left on your needles. Then, pull the yarn through the last loop and weave in the ends to your hat.

You may need to increase (every two stitches k2tog) or decrease (every 10 stitches k2tog) the number of stitches you need to knit together as a decrease depending on the yarn you’re using.

What Size Baby Hat Should You Knit?

  • For a baby due in the spring, knit a size 6-9 month to wear this year, or a size 18-24 month for next year.
  • For a baby due in the summer, knit a hat in 3-6 month size to wear this year, or 18-24 month for next year.
  • For a baby due in the fall, knit a hat in 0-3 or 3-6 month size to wear this year, or 24-month size for next year.
  • For a baby due in the winter, knit a hat in 0-3 or 3-6 size to wear this year, or 12-month or 24-month size for next year.
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