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What hat size is 21 inches?

A 21-inch head circumference is a fitted size 6 ⅝, which is 53.3 cm. Here is how that translates across sizing systems and brands.

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21 inches to hat size

Divide the head circumference by pi: 21 ÷ 3.1416 = 6.68. The nearest eighth is 6 ⅝, so a 21-inch head wears a size 6 ⅝. Because 6.68 sits between two sizes, go up to 6 ¾ for fitted caps and felt hats. That is UK 6 ½, EU 53 and usually a letter size XS.

21 inches to hat size
Fitted sizecmInchesUKLetter
6 ½ 51.9 20 ⅜ (20.42) 6 ⅜ XS
6 ⅝ 52.9 20 ⅞ (20.81) 6 ½ XS
6 ¾ 53.9 21 ¼ (21.21) 6 ⅝ S
6 ⅞ 54.9 21 ⅝ (21.6) 6 ¾ S
7 55.9 22 (21.99) 6 ⅞ M
7 ⅛ 56.9 22 ⅜ (22.38) 7 M
7 ¼ 57.9 22 ¾ (22.78) 7 ⅛ L
7 ⅜ 58.8 23 ⅛ (23.17) 7 ¼ L
7 ½ 59.8 23 ½ (23.56) 7 ⅜ XL
7 ⅝ 60.8 24 (23.95) 7 ½ XL
7 ¾ 61.8 24 ⅜ (24.35) 7 ⅝ XXL
7 ⅞ 62.8 24 ¾ (24.74) 7 ¾ XXL
8 63.8 25 ⅛ (25.13) 7 ⅞ 3XL
8 ⅛ 64.8 25 ½ (25.53) 8 3XL
8 ¼ 65.8 25 ⅞ (25.92) 8 ⅛ 3XL

21-inch head: size by brand

Brands that sell stretch-fit or letter sizes use ranges. For a head of exactly this size:

  • New Era 59FIFTY: 6 ⅝
  • Flexfit: Youth
  • Nike: S/M
  • Stetson: X-Small

Related sizes

Fit tips

  • Measure with the tape where the hat will sit: across the middle of the forehead and about 1 cm above the ears.
  • If your tape reads a little over 21 inches, use the exact number in the calculator. Every eighth of an inch of diameter is about ⅜ inch of circumference.
  • Round up for fitted caps and felt hats. Round down for stretch-fit caps and beanies.

How to measure your head

  1. 1 Use a soft tape measure, or a string and a ruler.
  2. 2 Wrap it around your head where the hat will sit: about 1 cm (⅜ in) above your ears and across the middle of your forehead.
  3. 3 Keep the tape level and snug, not tight. Do not pull it in.
  4. 4 Read the number where the tape overlaps. Measure two or three times and use the largest value.
  5. 5 Type the number into the calculator, or find it in the chart.
How to measure

Frequently asked questions

What size hat fits a 21-inch head?

A fitted 6 ⅝, which is UK 6 ½ and EU 53. In letter sizes it is usually a XS.

Is a 21-inch head big?

No. It is on the small side for an adult and a typical size for teenagers and women with a smaller head.

How many cm is a 21-inch head?

21 inches is 53.3 cm.

Related charts

All charts