You can find press and casual photos pretty easily of Amir Johnson together with Chris Bosh, who is a fairly certain 6'11-6'11.5 or Tyler Hansbrough, who is a fairly certain 6'9-6'9.5 (both in shoes, obviously).
He's very clearly taller than Hansbrough and very clearly shorter than Bosh. I'm confident that Johnson's height in shoes is between 6'10 and 6'11.