A Guide to Hat Sizing

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A Guide to Hat Sizing

This page will help you obtain accurate head measurements for babies, children and adults, and in turn help you choose the right size for the perfect fit.

Head sizes vary from person to person, but generally fall into the size categories below. To be sure though, one size does not fit all, or even most!

Getting Started

To measure your head circumference, wrap a tape measure around the widest part of your head – over your hair, starting from your forehead, above your ears and around the back, then round to the front again.

Make sure the tape measure is snug – a Hat should fit snuggly; not too tight or too loose. The circumference is the measurement used for Hat sizes, and is the measurement given for the brim of the Hat.

The length of a Hat will vary between styles, but to know the length of your head in relation to the pattern, measure from your crown to the base of your ear and this will give you your ideal head length for Hats.

Hat patterns contain measurements and sizing based on gauge, and number of stitches and rows – if your working gauge is tighter or looser than that given, you may need to adjust your number of stitches accordingly, or adjust your needle or hook size.

Diagram 1 shows arrows indicating both directions we need to measure

Choosing the Right Size

The finished measurements for Hats listed in the patterns may be slightly smaller than those given below, to ensure the fabric is stretched slightly for a snug fit – this is known as ‘negative ease’. The actual difference between the finished size of a Hat compared to the desired size is usually 2 to 3 inches, 5 to 7.5 centimetres, or roughly 12%, – this is the normal amount of negative ease included within Woolly Wormhead knit and crochet Hat patterns.

All Woolly Wormhead patterns list both the Finished Size – i.e. the finished circumference of the Hat, and the To Fit Size – i.e. the head circumference size of the intended wearer. With this information you can decide which size is best for you if you fall between sizes, or if you prefer more or less negative ease in your Hats.

Besides negative ease, another factor that determines fit is personal choice. Some people like their Hats with little or no negative ease for a more casual look, some people prefer a tighter fitting Hat for a sportier look. This preference in fit is also affected by the style of the Hat, so do consider how the Hat will be worn in relation to the measurements given in the pattern. All Woolly Wormhead patterns include a range of sizes as well as the finished measurements to help determine which size is the best one to make. You’ll also find notes on adjustment, where applicable, to help you achieve a wider range of sizes outside of the pattern or fine tune the pattern to your size.

Typical Sizes

Below is a chart showing typical head sizes by age. The measurements given are in both metric and imperial, and cover head circumference, head length and mid-ear to mid-ear points for positioning earflaps.

Find the measurements provided in text format for each size below the chart.

These measurements were gained with the help of the Head Measuring Game and from my own experience from years of travelling to teach Hat design and hosting Hat clinics.

Diagram 2: this chart shows the typical measurements by age

Head Circumference by age in metric

Preemie: 30.5 centimetres

Newborn: 35.5 centimetres

6 months: 40.5 centimetres

12 months: 45.5 centimetres

Child, teenager or small adult: 50.5 centimetres

Average adult: 56 centimetres

Large adult: 61 centimetres

Extra large adult: 66 centimetres

Head Circumference by age in imperial

Preemie: 12 inches

Newborn: 14 inches

6 months: 16 inches

12 months: 18 inches

Child, teenager or small adult: 20 inches

Average adult: 22 inches

Large adult: 24 inches

Extra large adult: 26 inches

Head length by age in metric

Preemie: 11 centimetres

Newborn: 12.5 centimetres

6 months: 14.5 centimetres

12 months: 16.5 centimetres

Child, teenager or small adult: 18.5 centimetres

Average adult: 21 centimetres

Large adult: 23.5 centimetres

Extra large adult: 25 centimetres

Head length by age in imperial

Preemie: 4.25 inches

Newborn: 5 inches

6 months: 5.75 inches

12 months: 6.5 inches

Child, teenager or small adult: 7.25 inches

Average adult: 8.25 inches

Large adult: 9.25 inches

Extra large adult: 10 inches

Mid-ear to mid-ear across the front then back by age in metric

Preemie: 15.75 centimetres, 14.75 centimetres

Newborn: 19 centimetres, 16.5 centimetres

6 months: 22.25 centimetres, 18.25 centimetres

12 months: 24.5 centimetres, 21 centimetres

Child, teenager or small adult: 27.75 centimetres, 22.75 centimetres

Average adult: 31.75 centimetres, 24.25 centimetres

Large adult: 35 centimetres, 26 centimetres

Extra large adult: 38 centimetres, 28 centimetres

Mid-ear to mid-ear across the front then back by age in imperial

Preemie: 6.25 inches, 5.75 inches

Newborn: 7.5 inches, 6.5 inches

6 months: 8.75 inches, 7.25 inches

12 months: 9.75 inches, 8.25 inches

Child, teenager or small adult: 11 inches, 9 inches

Average adult: 12.5 inches, 9.5 inches

Large adult: 13.75 inches, 10.25 inches

Extra large adult: 15 inches, 11 inches

eta/ this page was updated on 25th January 2022 to include full text measurements to accompany the sizing chart, and to include additional notes on choosing the right size.

eta2/ this page was updated on 13th January 2023 to sizes up to a 26 inch, 66 centimetre circumference head.

Woolly Wormhead

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  1. Rede Batcheller

    That is absolutely amazing! I’ll probably have something else to say when I’ve spent some time knitting and then The Hub gets to try it on and . . . One thing confuses me: where it says "across the front then back". I think I understand "mid-ear to mid-ear", and "by age in [measurement type]". Now, you must keep in mind that a lot of things confuse me! Does this mean measure twice — once across the front and once across the ack and they should be equal? — or? I’m an inches i.e. imperial person. I use mm metric for scaling — quite handy! But if worse gets even worse I’ll deal in mm metric . . .

    • Woolly Wormhead

      This means you measure twice – our ears are not centrally placed on our heads!

      So the mid-ear to mid-ear measurement taken at the front, across our forehead, will be greater than the mid-ear to mid-ear measurement when taken across the back 🙂

  2. Geraldine Watson

    How do I apply these measurements when knitting a Baby Bonnet for a newborn please. It’s difficult when you dont have a baby to take actual head measurements?

    • Woolly Wormhead

      Follow the size a newborn given in the table 🙂 If you know the parents are larger headed, or conversely have smaller heads than average, then it’s a safe bet that the baby might be the same. But otherwise, go with the newborn size that’s listed.

      One thing about babies and kids is that they always grow, so it’s better to err on the side of too big rather than too small. The first year is when we see the most head growth!


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