If you are looking for a fitted hat, then you’ll need to know what size your head is.
Here’s a quick guide to measuring your head:
Put a tape measure around your head where the hat will sit, so that is above the ears, above the eyebrows and just below the bump at the back of your head.

In the photo above, the measurement is just under 60 centimetres, so the size to choose is large.

The size to choose for this measurement (above) of just over 54cm is small.
Here’s a handy size guide:
Size | Small | Medium | Large | Ex Large | |||
Size UK | 6 3/4 | 6 7/8 | 7 | 7 1/8 | 7 1/4 | 7 3/8 | 7 1/2 |
In cms | 55 cm | 56 cm | 57 cm | 58 cm | 59 cm | 60 cm | 61 cm |
In inches | 21 5/8” | 22” | 22 1/2” | 22 3/4” | 23 1/4” | 23 5/8” | 24” |