You've found a hat you love, you now need to ensure you've got the right fit. 

To determine your head size, measure the circumference of your head by wrapping a tape measure around your head. Level the tape measure by placing it 1cm above your eyebrows and around the back of your head, with it sitting on the occipital bunmost protruding part of the back of your head. Hold the tape firmly, but do not pull tightly. The measurement on the tape measure is your head size. 

It's best to measure rather than referring to other brands of hats, to ensure the best fit. All brands measure their hats differently and occasionally, there can be a slight variation, depending on the fabrication or material. 

As a guide, choose:

56cm for small

57.5cm for Medium

59cm for Large