Royal Caribbean’s Quantum class is five ships in two variants. The three original Quantum-class hulls — Quantum, Anthem and Ovation of the Seas — are each 168,666 gross tons carrying 4,180 guests across 14 passenger decks. The two Quantum Ultra hulls, Spectrum of the Seas at 169,379 tons and Odyssey of the Seas at 167,704, carry 4,246 and 4,200 respectively. The class was designed around enclosed space for cooler-weather itineraries, which is why it carries about a quarter fewer guests than an Icon-class ship on a vessel large enough for the full dining and entertainment range.
Royal Caribbean sells the Quantum class in two flavours, Quantum and Quantum Ultra, and the largest Ultra hull beats the base ships by 713 gross tons and 66 guests. That is not a generation. It is a rounding error with a marketing name. What the class actually is — the fleet’s answer to weather — is the part worth understanding before you book.
Which Quantum-class ship to book
Book Anthem of the Seas if you are sailing from the north-east or Europe. 168,666 gross tons, 4,180 guests at double occupancy, 14 passenger decks. In service since 2015. It is the hull that spends most of its life on itineraries where the weather is a genuine variable, which is exactly what this class was designed for.
Book Odyssey of the Seas for the newest hull. In service since 2021, 167,704 gross tons, 4,200 guests, 14 passenger decks. It is a Quantum Ultra ship and, at 962 tons under Spectrum, the smallest of the five by tonnage while carrying more guests than the three base hulls.
Book Quantum of the Seas if you want the original. The lead ship, in service since 2014, 168,666 tons and 4,180 guests. Identical on paper to Anthem and Ovation.
Spectrum of the Seas is the largest, at 169,379 gross tons carrying 4,246 guests — the biggest capacity in the class. It is also the hull most often deployed in Asia, so for most travellers the itinerary decides this one rather than the specification.
The honest summary: these five ships are close enough that picking between them on tonnage is a waste of an afternoon. Pick the one sailing where you want to go, on a date that works. The class is the decision; the hull is not.
The five ships, and what Ultra actually means
Quantum class — three ships, identical specifications. Quantum of the Seas (2014), Anthem of the Seas (2015) and Ovation of the Seas (2016). Each is 168,666 gross tons, carries 4,180 guests at double occupancy, and has 14 passenger decks. Genuinely identical, which is unusual in this fleet.
Quantum Ultra — two ships, marginally different. Spectrum of the Seas (2019) at 169,379 tons and 4,246 guests, and Odyssey of the Seas (2021) at 167,704 tons and 4,200 guests. Both also have 14 passenger decks.
So Ultra means one hull that is 713 tons larger than the base ships and one that is 962 tons smaller. The whole class fits inside a one percent band on tonnage, and every ship in it has the same number of passenger decks. Treat Quantum and Quantum Ultra as one class with a badge, because that is what the numbers say.
This is worth saying because deck counts usually do not hold across a Royal Caribbean class. In the Icon class they do not. Here they do, and it is one of the few places you can safely reason from the class to the ship.
What the class is built for
Enclosed space, and a lot of it. The Quantum class was designed around the problem the Caribbean-focused classes ignore: what people do on the ship when it is too cold to be outside. That is why it works on Alaska sailings in a way the open-deck classes do not, and why it holds up on a north-east departure in shoulder season.
A quarter fewer people than the flagships. 4,180 to 4,246 guests against 5,610 on an Icon-class ship. The venue count does not drop proportionally, so the practical effect is shorter queues for the same range of things to do. This is the most underrated trade in the Royal Caribbean fleet.
Where it is the wrong answer. If you want the waterpark and the neighbourhood layout that the newest ships are built around, the Quantum class does not have it and no amount of size makes up for that. That is a different holiday, not a smaller version of this one.
Before you compare it to anything else
Gross tonnage is enclosed volume rather than weight, so it is the right number for comparing how much ship there is. Guest counts here are at double occupancy, two to a cabin, and a fully sold ship carries more once the third and fourth berths go.
One caution that applies beyond this class: the fact that all five Quantum hulls share a deck count is the exception, not the rule. Elsewhere in the fleet ships with identical tonnage differ by two decks. Check the figure for the exact ship rather than the class whenever it matters to the booking.
Common questions
How many Quantum-class ships are there?
Five. Three Quantum class: Quantum of the Seas (2014), Anthem of the Seas (2015) and Ovation of the Seas (2016). Two Quantum Ultra: Spectrum of the Seas (2019) and Odyssey of the Seas (2021).
What is the difference between Quantum and Quantum Ultra?
Ultra is an evolution of the same platform rather than a new design. The three original hulls are identical at 168,666 gross tons and 4,180 guests; Spectrum is slightly larger at 169,379 tons and 4,246 guests, Odyssey slightly smaller at 167,704 tons and 4,200. All five run to 14 passenger decks.
Which Quantum-class ship is the biggest?
Spectrum of the Seas at 169,379 gross tons. The whole class sits within about one percent of itself.
Are Quantum-class ships good for Alaska?
Yes, and that is close to the point of the class. It was built with more enclosed and glazed space than the Caribbean-focused classes, which is what you want when the scenery is outside and the weather is not cooperating.
Is a Quantum-class ship less crowded than an Icon-class ship?
It carries 4,180 to 4,246 guests against 5,610 on an Icon-class ship, so roughly a quarter fewer people, on a vessel still large enough for a full range of venues.
The Quantum class is what to book when you want a large ship without the crowd that usually comes with one, or when the weather is going to be part of the trip. It rarely wins a spec-sheet comparison and it regularly wins the actual week.
We book these constantly and we will tell you which of the five is sailing your dates rather than selling you the newest thing on the page. The full fleet is on our Royal Caribbean page, and our cabin guide is the sensible next step.