A measure of cubic space per passenger, space ratio is derived by dividing gross tons by the number of passengers, double occupancy (by contrast, total occupancy counts for all occupied berths in a cabin, including third and fourth beds).
The greater the space ratio, in theory, the less crowded the ship feels. So if you want a ship that does not feel crowded, choose one with a generous space ratio. On the other hand, if you’re worried about feeling all alone, choose a ship with a smaller space ratio.
Typically, small luxury ships have greater space ratios than do large ships. Silversea Cruises’ 388-passenger Silver Shadow, for example, measures a mere 28,258 gross tons but features a space ratio of 73 while the world’s largest cruise ships, Royal Caribbean International’s Freedom-class vessels, feature a space ratio of only 44.
The standard measure of a cruise ship, “gross ton,” dates back to the 14th century, when a tun was a large wine cask with a capacity of 252 old wine gallons. Today, a gross ton is equal to 100 cubic feet of enclosed space, thus ships “measure,” not “weigh,” in gross tons.