A char(2) takes 2 bytes, a varchar(2) takes 2-4 bytes, A char(3) takes 3 bytes, a varchar(3) takes 2-5 bytes, etc. I'll usually switch around 4-6 characters, unless the column will always have a certain number of characters, in which case it's char.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability