I bought this hat for my 6 year old son who really wanted one like this to wear at school since it gets sunny in California pretty much year round and this last summer was really sunny and hot some days. He loves it. He didn't get to wear it much since I bought it a little late in the season. I compared a lot of hats of this design and was looking for good coverage, not simply a baseball cap with a back which leaves a gap at the sides and, well, looks like a baseball cap with a back. This was the best price for the best design. This hat also comes with a metal clip to clip it onto your shirt on windy days, and a drawstring to cinch it in back to make it a bit smaller for good fit.
There's a black felt lining for a sweatband and 4 grommets for venting, along with a side vent strip on each side. The hat is 100% polyester and says "one size fits all" and is made in China. The circumference is 21 1/2 " or 54 1/2 cm around uncinched. The bill is 3 1/4" long (the dimension that sticks out perpendicularly from the hat and shades your face). The back flap is 8 1/2" in length.
The only caveat is that I wish it came in a stone color, but this is a nice dark khaki color that goes with everything as well. I highly recommend this hat if your head is 54 cm in circum. or less.