List of rail transport modelling scale standards

List of rail transport modelling scale standards

This page lists the most important 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.


Scale Standards


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:

  • no letter = standard gauge (prototype: 1,250–1,500 mm/49.2–59.1 in)
  • m = metre gauge (prototype: 850–1,250 mm/33.5–49.2 in)
  • e = narrow gauge (prototype: 650–850 mm/25.6–33.5 in)
  • i = industrial (prototype: 400–650 mm/15.7–25.6 in)

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.

Scale Ratio Standard gauge m e i Notes
Z 1:220 6.5 mm (0.256 in) 4.5 mm - - Based on Märklin factory standards.
N 1:160 9 mm (0.354 in) 6.5 mm 4.5 mm - Based on Arnold factory standards.
TT 1:120 12 mm (0.472 in) 9 mm 6.5 mm 4.5 mm -
H0 1:87 16.5 mm (0.650 in) 12 mm 9 mm 6.5 mm "Half Zero"
S 1:64 22.5 mm (0.886 in) 16.5 mm 12 mm 9 mm -
0 1:45 32 mm (1.260 in) 22.5 mm 16.5 mm 12 mm  
1 1:32 45 mm (1.772 in) 32 mm 22.5 mm 16.5 mm -
II 1:22.5 63.5 mm (2 12 in) 45 mm 32 mm 22.5 mm  
III 1:16 89 mm (3 12 in) 63.5 mm 45 mm 32 mm -
V 1:11 127 mm (5 in) 89 mm 63.5 mm 45 mm -
VII 1:8 184 mm (7 14 in) 127 mm 89 mm 63.5 mm -
X 1:5.5 260 mm (10 14 in) 184 mm 127 mm 89 mm -


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.

There are two NMRA standard sheets where the scales have been defined. NMRA standard S-1.2 covers the popular model railway scales and S-1.3 defines scales with deep flanges for model railways with very sharp curves or other garden railway specific design features.

In certain NMRA scales an alternative designation is sometimes used corresponding the length of one prototype foot in scale either in millimetres or in inches. For instance, 3.5 mm scale is the same as HO. It should be noted that for H0 and 0 -scales, NMRA uses letter 'O' whereas NEM uses the number zero (H0 instead of HO).

NMRA has defined alternative, more prototypical, track and wheel system standards in standard sheet S-1.1 for the purposes of reproducing the prototype proportions in scale model more realistically. These model railway standards are based on the full size prototype standards and the scale model operational reliability is therefore reduced in comparison to the models conforming to the normal NMRA standards. Proto and Finescale rails and wheels are generally not compatible with the normal scale model railway material with the same scale ratio.

Proto scale was originally developed by the Model Railway Study Group in Great Britain in 1966 and later adopted into NMRA standards with modifications necessary for the North American prototype railway standards. Proto scale reproduces faithfully the prototype wheel tread profile and track work used by the Association of American Railroads and the American Railway Engineering Association.

Finescale reproduces the prototype wheel tread profile and track work used by the Association of American Railroads and the American Railway Engineering Association with minor compromises for performance and manufacturability.

NMRA Popular Railway Scales

Scale Ratio Gauge Notes
Z 1:220 0.257 in (6.53 mm)
0.256 in (6.5 mm)
NMRA does not give any other dimensions for Z-scale apart from the gauge
Nn2 1:160 0.177 in (4.5 mm)
4.5 mm (0.177 in)
narrow gauge
Nn3 1:160 0.256 in (6.5 mm)
6.5 mm (0.256 in)
narrow gauge
N 1:160 0.353 in (8.97 mm) -
TT 1:120 0.470 in (11.94 mm)
0.473 in (12.0 mm)
0.472 in (12 mm)
12 mm (0.472 in)
HOn2 or 3.5 mm 1:87.1 0.276 in (7 mm) narrow gauge
HO or 3.5 mm 1:87.1 0.650 in (16.5 mm) -
OO or 4 mm 1:76.2 0.750 in (19.05 mm) -
Sn3 or 3/16" 1:64 0.563 in (14.3 mm) narrow gauge
S or 3/16" 1:64 0.883 in (22.42 mm) -
On2 or 1/4" 1:48 0.5 in (12.7 mm) narrow gauge
On30 or 1/4" 1:48 HO-track narrow gauge
On3 or 1/4" 1:48 0.750 in (19.05 mm)
19.4 mm (0.764 in) (?)
narrow gauge
O or 1/4" 1:48 1.25 in (31.75 mm) -
#1n3 or 3/8" 1:32 1.125 in (28.6 mm) narrow gauge
# I or 3/8" 1:32 1.766 in (44.85 mm) -
Fn3 or 15 mm 1:20.32 #1-track narrow gauge
F or 15 mm 1:20.32 2.781 in (70.64 mm) Identical to Proto 20.32 except the wheel flange depth
3/4" 1:16 3 12 in (89 mm) -
1" 1:12 4 34 in (121 mm) -

NMRA Deep Flange Scales

Scale Ratio Gauge Notes
SHR or 3/16" 1:64 0.865 in (21.97 mm)
vs 0.865 in (22 mm)
O27 - - Same as OHR but models 10% smaller
on the same track gauge
OHR or 1/4" 1:48 1.25 in (31.75 mm) -
G or 3/8" 1:32 1.772 in (45 mm) -
G 1:29 1.772 in (45 mm) -
G 1:24 1.772 in (45 mm) -
G 1:22.5 1.772 in (45 mm) -
G 1:20.3 1.772 in (45 mm) -

NMRA Proto Scales

Scale Ratio Gauge Notes
Proto:20.32 1:20.32 2.781 in (70.64 mm)
vs 2.781 in (70.64 mm) (?)
Proto:20.32n3 1:20.32 1.772 in (45 mm) -
Proto:32 1:32 1.766 in (44.85 mm) -
Proto:32n3 1:32 1.125 in (28.6 mm) -
Proto:48w5 1:48 1.25 in (31.75 mm) Russian prototypes
Proto:48 1:48 1.177 in (29.9 mm) -
Proto:48n3 1:48 0.750 in (19.05 mm) -
Proto:64 1:64 0.883 in (22.42 mm) -
Proto:64n3 1:64 0.563 in (14.3 mm) -
Proto:87 1:87.1 0.649 in (16.48 mm) -
Proto:87n3 1:87.1 0.413 in (10.5 mm) -

NMRA Finescale

Scale Ratio Gauge Notes
Fine:HO 1:87.1 0.649 in (16.48 mm) -
Fine:HOn3 1:87.1 0.413 in (10.5 mm) -
Fine:TT 1:120 0.470 in (11.94 mm)
0.472 in (12 mm)
Fine:TTn3 1:120 0.353 in (8.97 mm) -
Fine:N 1:160 0.353 in (8.97 mm) -
Fine:Nn3 1:160 0.250 in (6.35 mm) -


The main railways in Great Britain use the international standard gauge of 1,435 mm (4 ft 8 12 in) but the loading gauge is narrower and lower than in the rest of Europe with the same standard gauge. This is one of the main reasons why the country has traditionally used its own distinctive model railway scales which can rarely be found outside the British Isles.

When H0 scale was being introduced, the motors available were too large[1][2] to fit in scale-sized bodies and so as a compromise the scale was increased from 3.5mm to 4mm to the foot, but the gauge was not changed so other elements could be shared. For 00 therefore the track is narrower than it should be for the scale used. In more recent times, small motors have become available and so the advent of EM and ProtoFour scales correct this anomaly by adopting a larget track gauge.

The globally more-widespread international NEM and NMRA scale standards are relatively rare in Great Britain and used almost exclusively by those modelling foreign prototypes.

Scale Ratio Gauge Notes
000 or 2 mm 1:152 9.42 mm (0.371 in) An early predecessor of small scales like N. Developed before World War II and became somewhat popular in the 1950s. No commercial products available. Today The 2mm Scale Association is the force behind the scale and 2mm scale has become a finescale alternative to the British N-scale.
N 1:148 9 mm (0.354 in) A British adaptation of N-scale for modelling British prototypes with a smaller loading gauge. Has a track gauge error of approximately -7%. Hobbyists who model European or American prototypes in Britain, use the standard N-scale with the scale ratio 1:160.
TT/TT3 or 3mm 1:102 12 mm (0.472 in) Introduced by Triang in 1957 as a British adaptation of the American TT scale. Later Triang dropped this scale in favour of N scale and today there is no commercial following. Has a track gauge error of approximately -15%.
H0 or 3.5mm 1:87 16.5 mm (0.650 in) H0 scale was introduced in Britain in the 1920s. No commercial following and used by only a small number of modellers to model the British prototype.
00 or 4mm 1:76 16.5 mm (0.650 in) The most popular railway modelling scale in Britain. Has a track gauge error of approximately -12.5%.
EM or 4mm 1:76 18.2 mm (0.717 in) This gauge is represented by the EM Society (in full, Eighteen Millimetre Society). 00 track (16.5 mm) is the wrong gauge for 1:76 scale, but use of an 18.2 mm (0.717 in) gauge track is accepted as the most popular compromise towards scale dimensions without having to make significant modifications to ready-to-run models. Has a track gauge error of approximately -3.5%.
P4 (Protofour)/S4 (Scalefour) or 4mm 1:76.2 18.83 mm (0.741 in) Uses a track gauge of 18.83 mm which represents an exact scaling down of the prototype at 4 mm to 1 ft scale. As a scaling down of prototype dimensions with, in the case of P4 standards but not S4 standards, only slight modifications from true proportionality, the standards also specify wheel profile and other track dimensions as well as the track gauge. The standards set by the Scalefour Society are now applied to other prototypical track gauges (such as Irish Broad gauge).
O14 1:43.5 14 mm (0.551 in) For accurately representing 2 ft narrow gauge in 7mm scale.
0 or 7mm 1:43.5 32 mm (1.260 in) Three sub-standards: Coarse, Unified and Fine. Has a track gauge error of approximately -3%.
ScaleSeven (S7) 7mm 1:43.5 33 mm (1.299 in) A finescale scale represented by The ScaleSeven group.


While there are Japanese model railway manufacturers that export their products to other parts of the world and follow the scale standards of the export destinations, in Japan there are several domestic scales that are popular in the country but virtually unknown elsewhere. International NEM and NMRA scales are also used by some Japanese modellers. The main reason for the domestic scales different from international standards is the smaller prototype loading gauge and unusual gauges of Japanese railways: 600 mm (1 ft 11 58 in), 762 mm (2 ft 6 in) and 1,067 mm (3 ft 6 in) (International standard gauge of 1,435 mm/4 ft 8 12 in is also used).

Scale Ratio Gauge Notes
T 1:450
3 mm (0.118 in) Launched at 2006 Tokyo Toy Show by Eishindo Co.
ZZ 1:300 4.8 mm (0.189 in) Introduced 2005 by Bandai
ZJ 1:220 6.5 mm (0.256 in)  
N 1:150 9 mm (0.354 in) The most popular scale in Japan. For the models of
Shinkansen high speed trains with a larger
loading scale, the international N scale standard ratio
of 1:160 is commonly used.
TT9 1:120 9 mm (0.354 in) Used also in New Zealand.
H0n2½ 1:80 9 mm (0.354 in) Used for 2 ft 6 in (762 mm) narrow gauge.
H0j 1:87 12 mm (0.472 in) Correct for 1,067 mm (3 ft 6 in) Japanese narrow gauge.
#13 1:80 13 mm (0.512 in) Correct for 1,067 mm (3 ft 6 in) Japanese narrow gauge.
H0 or #16 1:80 16.5 mm (0.650 in) Used for ready-to-run models.
Sn3 1:64 16.5 mm (0.650 in) Used for ready-to-run models.
- 1:50 20.5 mm (0.807 in) Static models mostly.
0j 1:45 24 mm (0.945 in) Correct for 1,067 mm (3 ft 6 in) Japanese narrow gauge.
35mm 1:30 35 mm (1.378 in) Used for 1,067 mm (3 ft 6 in) Japanese narrow gauge.
45mm 1:30 45 mm (1.772 in)  

Live Steam

Live Steam model railways are not standardized systematically by any single standardization body. There are, however, certain scales and gauges which have become de-facto standards and in some cases correspond to either NEM or NMRA standard scales. One example is the "IBLS" (International Brotherhood of Live Steamers), an informal organization which has published standards for some of the gauges. Many clubs have their own standards, which also may vary slightly from country to country. Hornby Railways have pioneered commercial model live steam in 00 (1:76 scale on 16.5mm gauge), the existing models are heated using a controllable electric current through the 2 running rails and have the steam pressure chamber in the model tender.

In addition the these scales, the United Kingdom has, over the last forty years, fathered a scale that is based on the predominant British narrow track gauge of 2 ft  (610 mm). Using 32 mm (1.260 in) - 0 gauge - track, there is an extensive range of 16 mm to the foot scale [1:19] live-steam and other types of locomotives, rolling stock and accessories. Many of these models are dual gauge, and can be converted to run on 45 mm (1.772 in) track (Gauge 1), and radio control is common. Locomotives in this scale are generally large and 'chunky', and can range from the tiny 0-4-0 seen on Welsh slate quarry lines all the way up to the very largest found in the UK, such as the ex-ACR NG/G16 Beyer-Garratt locomotives, seen running on the Welsh Highland Railway in North Wales. The hobby is supported by a number of 16mm live steam and electric traction builders, dominated by the likes of Roundhouse Engineering and Accucraft UK.

Scale Ratio Standard Gauge Notes
00 1:76 16.5 mm (0.650 in) Hornby produced.Generally regarded as the smallest scale for live steam.
O 1:45 32 mm (1.260 in) Popularly used for the small scale live steam.
No.1 1:32 45 mm (1.772 in) Popularly used for the small scale live steam. Corresponds to NEM 1 or NMRA #I.
No.3 1:22.6 63.5 mm (2 12 in) The smallest scale able to pull real passengers. Was one of the first popular live steam gauges, developed in England in the early 1900s. In terms of model railway operation, "Gauge '3' " is the largest (standard gauge) scenic railway modelling scale, using a scale of 13.5mm to the foot. The Gauge '3' Society represents this aspect of 2 1/2" gauge railway modelling with both electric and live steam operation. Gauge '3' corresponds to NEM II scale, also known as 'Spur II' in Germany.

The National 2.5" Association continues to support live steam passenger hauling in 2.5" gauge using MES Tracks. They use a 'scale' appropriate to the original prototype modelling both standard and narrow gauge locomotives to run on 2.5" track.

- 1:16 3 12 in (89 mm) A worldwide garden railroad scale. Corresponds to NEM III and NMRA 3/4".
- 1:12 4 34 in (121 mm) North America specific scale corresponding to NMRA 1" scale. 1:12 is one of the most popular backyard railway scales.
- 1:11 5 in (127 mm) Used outside North America. Corresponds to NEM V. One of the most popular garden railway scales.
- 1:8 7 14 in (184 mm) Used in North-Eastern USA, Canada and the world outside North America. Corresponds to NEM VII.
- 1:8 7 12 in (190.5 mm) Used in the Western parts of the USA.


There has been many short-lived and often promising model railway scales which are very much defunct nowadays. Quite often these were backed by only the company that created a new scale in the first place.

Scale Ratio Gauge Notes
K 1:180 8 mm (0.315 in) Introduced 1948 at the Hanover Fair in Germany by Prof. Walter M. Kersting.
OOO - 22 mm (0.866 in) Introduced in 1902 by Schoenner in Germany.
OO - 23 mm (0.906 in) Introduced in 1908 by Märklin and sold under name "Liliput-Eisenbahn" until 1932.
Z0 1:60 24 mm (0.945 in) Z0 or "Zwischen Null" (between 0) was in use in the 40's and 50's by several model railway manufacturers in Germany. Standardized in East German NORMAT model railway standard collection. Z0 was originally introduced in Czechoslovakia in 1938.
35mm 1:30 35 mm (1.378 in) 35 mm was in use in the 30's and 40's by several model railway manufacturers in Japan. 35 mm was introduced in 1930's. Late 1940s 35mm was replaced by O gauge.
No.2 1:27 Template:2 inches English scale, seven sixteenths of an inch to a foot, commercially used about 1900

See also

External links


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