I agree with those advising you try them on and wear them around the store for awhile before purchasing. I have more of an oblong shaped head and found that Arai helmets makes models for several different head shapes; i.e., round, oval, oblong. Buying the wrong helmet can be painful to the head as well as to the wallet!

 

"Because a Big O "Big Head"..."
Reminds me of a CPO initiation from the Essex

 

I have a size 8+ head as does everyone in my family.Most helmets run on the small size.HJC has a great fit in their XXXL sizes. Understand that heads are all different (Oval,oblong,rounder etc.) and fit is best achieved by visiting a store well stocked with multiple brands.I have almost 40 years riding,the last 15 grudgingly with a skid lid.There are even bigger models out there.Recently (2010) HJC brought out a XXXXX size.I just smile when a guy tells me he has a large noggin and then says something like 7 3/4.....that's a pinhead, amigo.....

 

its tough finding a store with a good supply, i hit a big show with all the manufacturers there and tryed helments on all day.

 

I spent years trying on full faced helmets convinced that my mild case of claustrophobia combined with a large head would prevent me from ever wearing one. Then I discoverd XXL and XXXL helmets. I bought a Joe Rocket FF helmet 2 years ago. Wear it primarily in cold weather or rain and it is the most comfortable helmet I have ever worn.

Try the metric dealers. They tend to have a greater variety of manufacturers and sizes in stock. I spent over an hour tyrying on helmets at a Honda/Yamaha/Kawasacki/Victory dealer. Found the right helmet but not the "right" color so they ordered it and I got it in a week.

There just aren't any shortcuts.