Cruise Ship Tonnage
One of the most confusing things about cruise ships is tonnage. There are many ways to rate ships, some referring to weight and others to actual size. To confuse things even more, there's an American system and a European system. There is deadweight tonnage, net registered tonnage, and displacement tonnage.
The only one that really matters to cruise ship passengers is Gross Registered Tonnage, also known as GRT. Broadly speaking, the GRT of a ship represents the capacity in cubic feet of all spaces within the hull (body of the ship) and the enclosed spaces above the deck available for passengers, crew and cargo divided by 100. So 100 cubic feet of capacity is equal to 1 gross registered ton.
Just a decade ago, some of the largest passenger ships were 35,000-48,000 tons. Those would now be considered small by today's standards! Most ships are now 50,000-80,000 GRT, with others 100,000+ and working up to a handful that are 135,000 GRT. That's a floating city!
Bigger usually means more bells and whistles. If you prefer more privacy, you may want to search for a mid-size or smaller vessel. Also note, that if you take a ships' GRT and divide by the number of passengers (generally listed at double occupancy), you will get the GRT/Passenger Ratio. The higher the number, the less crowded your experience should be. For example, a ship of 77,000 GRT with 2,200 passengers has a ratio of 35/1. If that same ship had only 1,750 passengers, the ratio would be 44/1. That more than likely means wider hallways, larger cabins, and less crowded lounges and public areas on the one with 1,750 passengers.
Pretty logical, but a good way to get an overview if you're researching on your own for which type of ship will serve your needs best.