List of rail transport modelling scale 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.

A 242A1 locomotive and standard gauge track at some model railway scales

Scale standards

NEM

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,[1] 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: 1,250–1,700 mm or 49.2–66.9 in)
  • m = metre gauge (prototype: 850–1,250 mm or 33.5–49.2 in)
  • e = narrow gauge (prototype: 650–850 mm or 25.6–33.5 in)
  • i = industrial (prototype: 400–650 mm or 15.7–25.6 in)
  • p = park railway (prototype: 300–400 mm or 11.8–15.7 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

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

ScaleRatioStandard gaugemeipNotes
T1:4803 mm (0.118 in)T gauge; the scale ratio of 1:450 in the UK.
Z1:2206.5 mm (0.256 in)4.5 mmStandard gauge based on the Märklin factory standards.
N1:1609 mm (0.354 in)6.5 mm4.5 mmStandard gauge based on the Arnold factory standards.
TT1:12012 mm (0.472 in)9 mm6.5 mm4.5 mm
H01:8716.5 mm (0.65 in)12 mm9 mm6.5 mm4.5 mm"Half O"
S1:6422.5 mm (0.886 in)16.5 mm12 mm9 mm6.5 mm
01:4532 mm (1.26 in)22.5 mm16.5 mm12 mm9 mm 
11:3245 mm (1.772 in)32 mm22.5 mm16.5 mm12 mm
II1:22.564 mm (2 12 in)45 mm32 mm22.5 mm16.5 mmStandard gauge known as Gauge 3 in the UK and known as Gauge 2½ on the Märklin factory standards from 1891.
III1:1689 mm (3 12 in)63.5 mm45 mm32 mm22.5 mm
V1:11127 mm (5 in)89 mm63.5 mm45 mm32 mm
VII1:8184 mm (7 14 in)127 mm89 mm63.5 mm45 mm
X1:5.5260 mm (10 14 in)184 mm127 mm89 mm63.5 mm

NMRA

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.

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. For HO and O -scales, NMRA uses the 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.

ScaleRatioModel gaugeNotes
Z1:2206.5 mm (0.256 in)NMRA does not give any other dimensions for Z-scale apart from the gauge
The s.g. is set nominally to gauge=6.5 mm; more exact to 1:220 would be 6.52 mm (0.257 in)
Nn21:1600.177 in (4.5 mm)
4.5 mm (0.177 in)
narrow gauge
Nn31:1600.256 in (6.5 mm)
6.5 mm (0.256 in)
narrow gauge
N1:1600.353 in (8.97 mm)standard gauge
TT1:1200.470 in (11.94 mm)
0.472 in (12 mm)
12 mm (0.472 in)
standard gauge
HOn2 or 3.5 mm1:87.17 mm (0.276 in)narrow gauge
HOn30 or 3.5 mm1.87.19 mm (0.354 in) (0.353 in.)narrow gauge--N scale track can be used
HOn3 or 3.5 mm1:87.110.5 mm (0.413 in)narrow gauge
HOm or 3.5 mm1:87.112 mm (0.472 in)narrow gauge--TT scale track can be used
HO or 3.5 mm1:87.10.65 in (16.5 mm)standard gauge
OO or 4 mm1:76.216.5 mm (0.65 in)standard gauge
Sn3 or 3/16″1:640.563 in (14.3 mm)narrow gauge
S or 3/16″1:640.883 in (22.43 mm)standard gauge
On2 or 1/4″1:4812.7 mm (0.5 in)narrow gauge
On30 or 1/4″1:48HO-tracknarrow gauge
On3 or 1/4″1:480.75 in (19.05 mm)
19.4 mm (0.764 in) (?)
narrow gauge
O or 1/4″1:481.25 in (31.75 mm)1.177 in (28.9 mm) is true standard gauge
No. 1n3 or 3/8″1:321.125 in (28.6 mm)narrow gauge
No. 1 or 3/8″1:321.766 in (44.85 mm)standard gauge
Fn3 or 15 mm1:20.32No. 1-tracknarrow gauge
F or 15 mm1:20.322.781 in (70.69 mm)Identical to Proto 20.32 except the wheel flange depth
3/4″1:163 12 in (89 mm)standard gauge
1″1:124 34 in (121 mm)

Note: to interpret the number in the left hand column, these examples illustrate:

  • 3.5 mm scale (HO): 3.5 mm scale measurement = 1 foot (304.8 mm) prototype. The ratio is therefore 1:87.08571, usually reported as 1:87.
  • 1" scale: 1" scale measurement = 1 foot prototype, the ratio is reported as 1:12.

NMRA deep flange scales

ScaleRatioGaugeNotes
SHR or 3/16″1:640.865 in (21.97 mm)
vs. 0.865 in (22 mm)
O27Same as OHR but models 10% smaller
on the same track gauge
OHR or 1/4″1:481.25 in (31.75 mm)
G or 3/8″1:321.772 in (45 mm)
G1:291.772 in (45 mm)
G1:241.772 in (45 mm)
G1:22.51.772 in (45 mm)
G1:20.31.772 in (45 mm)

NMRA proto scales

ScaleRatioGaugeNotes
Proto:20.321:20.3270.69 mm (2.781 in)NMRA[2][3]
Proto:20.32n31:20.321.772 in (45 mm)
Proto:321:321.766 in (44.85 mm)
Proto:32n31:321.125 in (28.6 mm)
Proto:48w51:481.25 in (31.75 mm)Russian prototypes
Proto:481:481.177 in (29.9 mm)
Proto:48n31:480.75 in (19.05 mm)
Proto:641:640.883 in (22.43 mm)
Proto:64n31:640.563 in (14.3 mm)
Proto:871:87.10.65 in (16.5 mm)
Proto:87n31:87.10.413 in (10.5 mm)

NMRA finescale

ScaleRatioGaugeNotes
Fine:HO1:87.10.65 in (16.5 mm)
Fine:HOn31:87.10.413 in (10.5 mm)
Fine:TT1:1200.470 in (11.94 mm)
0.472 in (12 mm)
Fine:N1:1600.353 in (8.97 mm)
Fine:Nn31:1600.25 in (6.35 mm)

British

The main railways in Great Britain use the international standard gauge of 4 ft 8 12 in (1,435 mm) 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[4] to fit in scale-sized bodies and so as a compromise the scale was increased from 3.5 mm to 4 mm 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. EM and P4 standards correct this anomaly by adopting a wider 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.

ScaleRatioGaugeNotes
000 or 2 mm1:1529.42 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 2 mm scale has become a finescale alternative to the British N-scale.
N1:1489 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 3 mm1:10212 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% (the rolling stock superstructures are too large for its gauge). Those models can drive on straight and curved sections of German BTTB Standard Gleis except crossings and switches.
H0 or 3.5 mm1:8716.5 mm (0.65 in)H0 scale was introduced in Britain in the 1920s, and although it stayed as the most common worldwide modelling scale, in Britain H0 has little commercial availability and is generally only used to model the British prototype by a small number of modellers.
00 or 4 mm1:7616.5 mm (0.65 in)The most popular railway modelling scale in Britain. The correct track gauge at the scale of 4 mm per foot should be approximately 18.8 mm. At 16.5 mm, it has a track gauge error of approximately -12.4%.
EM or 4 mm1:7618.2 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/S4 or 4 mm1:76.218.83 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. P4 contains an allowance for the tighter curves found on model railways in the wheel back-to-back and related dimensions. S4 removes this allowance, for a dead-scale representation of all trackwork dimensions. Both standards are now maintained by the Scalefour Society and are now applied to other prototypical track gauges (such as Irish broad gauge).
O141:43.514 mm (0.551 in)For accurately representing 2 ft narrow gauge in 7 mm scale.
0 or 7 mm1:43.532 mm (1.26 in)Three sub-standards: coarse, unified and fine. Has a track gauge error of approximately -3%.
ScaleSeven (S7) 7 mm1:43.533 mm (1.3 in)A finescale represented by The ScaleSeven group.

Japanese

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) are used, along with standard gauge of 1,435 mm (4 ft 8 12 in).

ScaleRatioGaugeNotes
T1:450
1:480
3 mm (0.118 in)Launched at 2006 Tokyo Toy Show by Eishindo Co.
ZZ1:3004.8 mm (0.189 in)Introduced 2005 by Bandai
Z or ZJ1:2206.5 mm (0.256 in) 
N1:150
1:160
9 mm (0.354 in)The most popular scale in Japan. For models of Shinkansen high speed trains and other systems
using standard gauge track, the international N scale standard ratio of 1:160 is commonly used.
TT91:1209 mm (0.354 in)Used also in New Zealand.
HOn2½1:809 mm (0.354 in)Used for 2 ft 6 in (762 mm) narrow gauge.
13 mm1:8013 mm (0.512 in)Correct for 1,067 mm (3 ft 6 in) Japanese narrow gauge.
HOj or #161:8016.5 mm (0.65 in)Used for ready-to-run models of 1,067 mm (3 ft 6 in) prototypes.
HO1:8716.5 mm (0.65 in)Used for models of Shinkansen high speed trains and other systems using standard gauge track.
HOn3-1/21:8712 mm (0.472 in)Correct for 1,067 mm (3 ft 6 in) Japanese narrow gauge.
Sn3½1:6416.5 mm (0.65 in)Used for ready-to-run models.
-1:5020.5 mm (0.807 in)Static models mostly.
OJ1:4524 mm (0.945 in)Correct for 1,067 mm (3 ft 6 in) Japanese narrow gauge.
O1:45
(1:40-1:42)
32 mm (1.26 in)1:40-1:42 used about 1930s.
35 mm1:3035 mm (1.378 in)Used for 1,067 mm (3 ft 6 in) Japanese narrow gauge.
# I or 45 mm1:3045 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 16.5 mm gauge), the existing models are heated using a controllable electric current through the two running rails and have the steam pressure chamber in the model tender.

In addition to 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 (1.26 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 16 mm live steam and electric traction builders, dominated by the likes of Roundhouse Engineering and Accucraft UK.

ScaleRatioStandard gaugeNotes
001:7616.5 mm (0.65 in)Hornby produced. Generally regarded as the smallest scale for live steam. Discontinued in 2011 due to poor sales and reliability of the units. The operating instructions from Hornby were incorrect and led to many locomotives being broken after derailing and crashing to the floor. There is still much interest and lively sales of secondhand sets. The 00 Live Steam Club also promotes the product.
O1:4532 mm (1.26 in)Popularly used for the small scale live steam.
No.11:3245 mm (1.772 in)Popularly used for the small scale live steam. Corresponds to NEM 1 or NMRA No. 1.
No.31:22.62 12 in (64 mm)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 13.5 mm to the foot. The Gauge '3' Society represents this aspect of 212" 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.

-1:163 12 in (89 mm)A worldwide garden railroad scale. Corresponds to NEM III and NMRA 3/4″.
-1:124 34 in (121 mm)North America specific scale corresponding to NMRA 1″ scale. 1:12 is one of the most popular backyard railway scales.
-1:115 in (127 mm)Used outside North America. Corresponds to NEM V. One of the most popular garden railway scales.
-1:87 14 in (184 mm)Used in North-Eastern US, Canada, Europe and other parts of the world. Corresponds to NEM VII.
-1:87 12 in (190.5 mm)Used in the Western parts of the US.
-1:7.51.6 in=1 ft. Used in the US, often finer-scale. Uses 7 12 in (190.5 mm) gauge.
-1:5287 mmUsed in Sweden. Also called the ÅHÅ scale.

Static model

ScaleRatioGaugeNotes
41 mm1:3541 mm (1.614 in)41 mm is used by several static model manufacturers, often for models of military subjects such as [railway guns][5] as 1:35 is a popular scale for rail modelling. 41 mm was introduced in the 2000s.[6][7]

[8]

Historical

There have 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.

ScaleRatioGaugeNotes
K1:1808 mm (0.315 in)Introduced 1948 at the Hannover Fair in Germany by Walter M. Kersting.
OOO22 mm (0.866 in)Introduced in 1902 by Schoenner in Germany.
Wesa1:11013 mm (0.512 in)Produced by WESA AG in Switzerland Between 1945 and 1950, used AC power.
Wesa1:10013 mm (0.512 in)Produced by WESA AG in Switzerland Between 1950 and 1966, used DC power.
OO23 mm (0.906 in)Introduced in 1908 by Märklin and sold under name "Liliput-Eisenbahn" until 1932.
Z01:6024 mm (0.945 in)Z0 or "Zwischen Null" (between 0) was in use in the 1940s and 1950s by several model railway manufacturers in Germany. Standardized in East German NORMAT model railway standard collection. Z0 was originally introduced in Czechoslovakia in 1938.
35 mm1:3035 mm (1.378 in)35 mm was in use in the 1930s and 1940s by several model railway manufacturers in Japan. 35 mm was introduced in the 1930s. Late 1940s 35 mm was replaced by O gauge.
No. 21:272 in (50.8 mm)English scale, 716 inch to 1 foot. Commercially used about 1900

See also

References

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