Fur timed hats/caps like these have been worn since the Middle Ages to Revolutionary war era. Some sources refer to this style as Canadian Hats These are 100% felt from Britian. Lined in Flax linen from the European mainland and hand stitched with linen thread. this one is in Green felt. with Muskrat trim and Pom size :21 !/2  

Hat Sizes

1.    Measure your head

Wrap the measuring tape around your head at the largest point over which your hat fits(above the ears).Put your finger where the tape overlaps and write down the number of inches.

The smallest standard hat size is 63/4, which corresponds to a head circumference of 21 1/8 inches. The largest standard size is 8 1/8, corresponding to a head circumference of 25 1/2 inches.  In general, a small hat ranges in size from 6 3/4 to 6 7/8.