Hat Sizing and How to Measure your Head
An average head size for a man is 58 cms in European Sizing or 7 1/8 UK sizing and 7 1/4 US sizing. The average head size for a lady is 55 cms. Probably the largest head size you will ever find, will be 64cms and the smallest 51cms.
How to measure your head
Take a measuring tape and place it around the circumference of the head, slightly above the ears.
Hat Measuring Chart