Rail transport modelling standards

This page lists the most relevant model railway scale standards in the world. Most standards are regional, but some have followers in other parts of the world outside their native region, most notably NEM and NMRA. While the most significant standardised dimension of a model railway scale is the gauge, a typical scale standard covers many more aspects of model railways and defines scale-specific dimensions for items like catenary, rolling stock wheels, loading gauge, curve radii and grades for slopes, for instance.

MOROP (the European federation of national model railway associations) is a European organisation which publishes NEM-standards. NEM-standards are used by model railway industry and hobbyists in Europe. The standards are published in French and German and both versions have an official status. Unofficial translations in English from third parties exist for certain NEM-standard sheets.

Model railway scales and gauges are standardized in NEM 010, which covers several gauges for each scale. Narrow gauges are indicated by an additional letter added after the base scale as follows:

For instance, a metre gauge model railway in H0-scale would be designated H0m. In German text letter 'f' (stands for Feldbahn) is sometimes used instead of 'i'. Letter 'e' is derived from the French word 'étroit' which translates to 'narrow'. NEM gauges are arranged conveniently to use normal gauge of smaller scales as narrow gauges for a certain scale. For instance, H0m gauge is the same as the TT scale normal gauge, H0e same as the N scale normal gauge and H0i same as the Z scale normal gauge

For H0 and 0 -scales, NEM uses the number zero or the letter 'O', whereas NMRA uses letter 'O' (H0 instead of HO). Regardless of whether a letter or number is used, the scale is the same.

The NMRA (National Model Railroad Association) standardized the first model railway scales in the 1940s. NMRA standards are used widely in North America and by certain special interest groups all over the world. To some extent NMRA and NEM standards are compatible, but in many areas, the two standards specify certain model railway details in somewhat incompatible ways for the same scale.

...
Wikipedia