Ship size in most trades is set by economics: build the largest vessel the cargo volume justifies. In LNG it is mostly set by what the shore can accept, and the classes that exist are fossils of particular decisions about particular terminals and canals.
Conventional: about 174,000 cubic metres
This is the standard newbuilding today, and the size most of the trading fleet clusters around. Roughly 295 metres long, 46 metres in beam, holding about 78,000 tonnes of LNG.
It is not the largest ship anyone could build. It is close to the largest that the majority of import terminals can receive — berth length, water depth, manifold arrangement and the reach of the loading arms all impose limits — and it fits the expanded Panama Canal locks, which matters enormously for US Gulf cargoes heading to Asia.
The size crept up over time in modest steps, from around 125,000 through 138,000, 145,000 and 155,000 cubic metres, each increment tracking what terminals could handle. That is the pattern: the fleet grows when the shore does.
Q-Flex and Q-Max
Qatar broke the pattern deliberately in the 2000s. Building at unprecedented scale, it ordered vessels far larger than anything then afloat: Q-Flex at roughly 210,000 to 217,000 cubic metres, and Q-Max at around 266,000.
The logic was straightforward. Qatar’s routes to Europe and Asia are long, its volumes were enormous, and unit shipping cost falls with size. Larger ships also justified equipment smaller ones could not: these were among the first LNG carriers with slow-speed diesel engines and onboard reliquefaction, so boil-off could be returned to the tanks rather than burned.
The cost was flexibility. Both classes are too wide for the Panama Canal even after its expansion, and a substantial number of terminals cannot receive them at all. A Q-Max is a ship for specific routes between specific berths, which was acceptable because Qatar built the berths.
Small-scale
At the other end, vessels from roughly 1,000 to 30,000 cubic metres do work no conventional carrier can.
They serve terminals that are too small, too shallow or too seasonal for a full cargo. They perform break bulk, taking a cargo delivered to a hub terminal and redistributing it in parcels to island and coastal markets. And they bunker ships that burn LNG as fuel, a market that barely existed fifteen years ago.
Small-scale vessels frequently use Type C pressure tanks rather than membranes, because at that size a pressure vessel is affordable and it removes the need for a boil-off handling system on a short voyage.
Floating facilities
FSRUs and FLNG units are built on carrier-like hulls but are not carriers in the trading sense. An FSRU is typically conventional-sized with regasification equipment aboard, and many are converted from older carriers. FLNG hulls are usually larger still, because a liquefaction plant has to fit on deck.
Some FSRUs retain the ability to trade as carriers when not moored, which makes them unusually flexible assets and unusually hard to classify.
Why the class matters when reading the fleet
A vessel’s capacity tells you where it can go, not just how much it carries. A 266,000 cubic metre ship is excluded from most of the world’s berths and from Panama. A 174,000 cubic metre ship can serve most terminals and transit most canals. A 30,000 cubic metre ship can enter ports the others cannot approach.
That is why the carrier directory reports capacity in cubic metres of liquid rather than converting to tonnes or energy: the physical volume is what the berth cares about. The voyage cycle explains what the ship then does with it.