I can never find any information about the height of the landing gear on any airliner(can you put it into feet and inches).And Is the height of the 747-8 landing gear around the same height as the 737 or airbus a320.
In general, the landing gear height is defined as the distance between the ground and the conjunction between main gear strut and the aircraft structure (fuselage, wing, nacelles, etc.).
The landing gear height of any aircraft varies depending the loading conditions and where you measure it (nose or main landing gear). This info is from the 747-8 Airplane Characteristics for Airport Planning document by Boeing.
Image from 747-8 Airplane Characteristics for Airport Planning by Boeing
Here, 'E' gives the height of the (main) landing gear attached to the fuselage.
The 747-400 gear is 1.91-2.47 meters tall, depending on model and loading, so it sits slightly higher in general than the 747-8.
The A320 (including neo) sits at 1.79-1.95 meters, so basically the same as the 747-8.
The 737 sits lower than the other two models, at 1.1 meters for the classic models, and 1.2-1.4 meters for the NG models.
It is interesting to note the similarities and differences. Designers want to keep the gear as short as possible to save weight, as well as to make maintenance or emergency evacuation easier. The gear still needs to be high enough to allow the aircraft to rotate on takeoff without striking the tail. Other aspects can be adjusted to maintain clearance for the engines. So even though the A320 and 747 are very different in size, they have the same gear height.
The 737 is different when it comes to gear length. The original 737 had engines that required much less height to clear the ground. The new engines on the classics and NG series needed more room, resulting in longer landing gear. However, the gear is still shorter than the other examples.