I have a question for you fellas. How high is the back of your cab roof from the back bed rail?

The reason I ask is I am in the market to buy a bed topper for my truck. I found a fella that has one but its offa 06 ram. I dont want to buy it if its taller than the cab (drag, road noise). I dont know much about the differences between the yrs for the ram and dont know if I could throw a tape on an 08+ and it be the same.

ANY help would be appreciated.