An average head size for a man is 59cm in European Sizing.
Approx 7 1/4 = Large Size UK sizing.
The average head size in the UK for a lady is 57 cms.
Head sizes and shapes differ from country to country with the smallest heads being in the Far Eastern countries and the largest in Germany. With regards to shape, these can be either very round or oval, with the far eastern countries having a rounder head and the western countries tending to have a more oval shape.
How to measure your head To check your hat size use a tape measure to measure around your head approximately two centimetres above the ears where your hat would sit comfortably then refer to the following chart:
Hats are sized to the nearest centimetre, so it is advisable to size up if your head falls between two measurements
Common sizes: Small-56cm. Medium-57cm. Large-59cm. Ex Large-60cm.
Burgess Hats Size Guide