The number of forty-foot equivalent units a modern cargo vessel can carry depends entirely on its size class, with ultra-large container ships capable of transporting tens of thousands of containers when measured in twenty-foot equivalents, which translates to roughly half that number in forty-foot boxes. Mega-ships deployed on major transoceanic lanes feature massive multi-layered deck configurations and deep hull cellular guides designed to stack thousands of 40-foot containers securely across numerous tiers, maximizing transport efficiency.