Really a 5u!!
OK...I bought this rack case to bring a 4U digital mixer that my band uses for in-ears on a flight. Was able to carry it on even though it's a little over the legal size for most carriers, it DID fit in the overhead bin of a Delta 757, 737. Now the best part is that I was also able to fit a half rack Shure in-ear receiver in the 5th space where there is normally a 1u cover that hides the handle. As long as it's not to deep, a half rack unit will fit. The wheels, handle, zippers are all top quality as well. Love this case!!!