What is the height of the Boeing 747-8 landing gear?
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.