From N Gauge wiki
N Gauge is a scale/track gauge that is used in model railways. The gap between the rails of the track is always 9mm (0.354 in); the name N gauge thus arising because the name for "nine" begins with "N" in most major European languages. An alternative name is 2mm scale, referring to 2mm being equivalent to one foot (30cm).
The models used on 9mm track are set to different scales depending on the prototype being modelled.
- 1:148 scale for UK prototypes
- 1:150 scale for standard Japanese prototypes, which in the real world run on 3' 6" tracks
- 1:160 scale for US, Canadian, European and Japanese Shinkansen prototypes
The actual correct scale for models on 9mm track would be 1:152.