Measuring the head is a starting point for
the entire sizing procedure. Due to varying shapes, heads that
are apparently the same size when measured by a tape may not
necessarily fit the same size helmet.
A small metal tape measure, or a cloth tape
may be used to make your initial measurement.
The circumference of the head should be measured
at a point approximately one inch above the eyebrows in front,
and at a point in the back of the head that results in the largest
possible measurement. Take several measurements, to make sure
you have the largest one.