There are three depth measurements that tend to be found in gun safe literature. Everybody does it differently. The first is the depth of the body. This is the measurement from steel to steel, front to back. The second is what I call the moving measurement. This is the measurement from the back of the safe to the front, including the additional depth of the dial, hinges, and handle hub. The third is the assembled depth. This is the measurement from the back to the front, including the additional depth of the handle spokes (which are tapered away from the safe) when installed.
You only need to be worried about the first two. If a company uses the first method, simply add 2" to that number. I rarely see gun safes with a body deeper than 28", which would put you at a maximum of 30". Most are 26".
The taller safes tend to have more height problems than depth problems when it comes to moving them.