How big is Queen Mary 2?
Queen Mary 2: 345 m (1,132 ft). Measured as length — overall length.
Source: Wikipedia — RMS Queen Mary 2
Where it sits
Among the 14 vehicles & ships on this page Queen Mary 2 ranks 3rd from the top by size. The largest in the group is Emma Maersk at 397 m, which is 1.15× the size of Queen Mary 2, while the smallest, Tesla Model 3, is 4.69 m.
Stand an adult of 1.7 m beside it and the ratio is 203×: you would need 202 people stacked head to foot to match its size.
In everyday distances
A football pitch is about 105 m long. Queen Mary 2 is 3.29× that, which puts it at 3.3 pitch lengths from end to end.
Walking at an easy 1.4 m/s you cover 345 m in 4.1 minutes. A jet at 900 km/h covers it in 1.4 seconds.
Next to its neighbours in size
The nearest thing larger than it in this collection is Allure of the Seas at 362 m (1,188 ft), 1.05× the size. Both figures are the same kind of measurement, so the gap is a fair one.
The nearest thing smaller is USS Nimitz at 333 m (1,092 ft), so Queen Mary 2 is 1.04× as big as it. They sit in the same group.
Against fixed yardsticks
Against three fixed yardsticks — Queen Mary 2 is 1.05× the size of Eiffel Tower (330 m); Queen Mary 2 is 11.5× the size of blue whale (29.9 m); Earth (12,742 km) is 36,933× the size of Queen Mary 2.
How this figure was taken
Vehicles are listed by overall length. Rockets are the exception and are given as full stack height standing on the pad. Everything is drawn standing upright so one scale holds.
How the sizes are taken. Each figure says what it measures — height, length, diameter or elevation — and for which individual or convention. Everything is drawn standing upright on one baseline so a single scale holds, including things that are long rather than tall. Values come from the linked Wikipedia article for each item.
Read the rest — common questions
How big is the Queen Mary 2?
345 m (1,132 ft), measured as length: overall length.
Where does the Queen Mary 2 rank among vehicles & ships?
Number 3 of 14 on this site, from Emma Maersk at 397 m down to Tesla Model 3 at 4.69 m.
What is the next size up?
Allure of the Seas, at 362 m, is 1.05× the size.
What is the next size down?
USS Nimitz, at 333 m, is 1.04× smaller.
How reliable is the figure?
It is taken from the cited Wikipedia article and states its basis (overall length). Values are rounded, and where individuals differ the figure is a representative one, so expect small differences from other sources.