How to Measure your Head for hat size
An normal head size for a man is 58 cms in Europe Size or 7 1/8 UK sizes and 7 1/4 US sizes. The normal head size for a lady is 55 cms. Probably the largest head size you will ever find, humpy dumpy will be 64cms and the smallest around 51cms.
sizes differ from country to country with the smallest skulls being in the Far East and the bigges in the Rhine land
How to measure your head for a hat size
Get a measuring tape and wrap it round the bit of the head where the hat fits a little bit above the ears.
Hat Measuring Chart