Scale and Gauge

Scale and gauge are key terms used in model railroads. What are they?

Scale is the ratio between the size of a model compared with the corresponding full size original. For example, a model train made as 1:48 scale means that 1″ of the model train equates to 48″ of the train it was modeled after.

Gauge is the distance between the inside of the two running rails of the track.

For trains to run on the same track, they must all have the same gauge, though not necessarily the same scale. Hence it’s possible to have slightly different “scale” models that will run on the same “gauge” rails, or, to have the same “scale” models with a slightly different “gauge” that cannot share the same track.

In the 1990’s there was a surge in modeler’s interest in narrow gauge railways (mostly logging and mining) as they allowed for much smaller curves and dramatic scenery. Modelers’ kit bashed larger scales to fit on existing smaller gauge tracks …. so if you run an N scale engine (1:160) on 6.5mm track (which is normally used for Z 1:220 trains) you can simulate running N scale on a 3 foot (vs. normal 4 foot 8 and a half inch) track. HOn3 is HO on special narrow gauge track but HOe is HO scale run on 9mm (N scale normally) track and On3 is O scale run on 16.5 mm (HO scale normally) track.
Below is a brief history of scale and gauges we found on the Internet.

The Development of Model Railway Scales and Gauges.

During the last century model railways were produced to scales and gauges at the whim of the manufacturer. Even when different makers used the same gauge, the variations in rail sizes, track standards, wheel standards and couplers precluded any intermixing of their models. Other than individuals building their own systems completely, “Model Railways” as we know them today were impossible. The first break-through came in 1891 at the Leipzig Toy fair when Maerklin introduced trains with a complete range of track parts with geometric curves, straights, points and crossings in 5 different scales:

No.5 gauge.120mmor 4 5/8″also known as V gauge.
No.4 gauge.75mmor 3″also known as IV, No.3 gauges.
No.3 gauge.67mmor 2 5/8″also known as III, II, IIa gauges.
No.2 gauge.54mmor 2 1/8″also known as II gauge.
No.1 gauge.48mmor 1 7/8″also known as I gauge.
And later:
No.0 gauge.35mmor 1 3/8″.This was introduced several years later, around the year 1900.

To all those people leaping to pen and paper to correct my figures, note that these gauges were measured from rail-center to rail-center, with a common rail-head width of 3mm. (1/8″) I believe these dimensions were originally inch measurements, later rounded to metric units. No.4 gauge is variously quoted at 3″ and 2 15/16″. Amusingly, when “American Flyer” in the USA decided to manufacture a new size, they looked at the Maerklin catalogue and selected the number 3 gauge. Unfortunately, they were not aware of the European method of gauge measurement and assumed that 2 5/8″ was the distance between the rails, rather than the center to center distance. They were not the only ones to make this kind of mistake. Some manufacturers, while they took up the standards, called 75mm gauge No.3 and 67mm No.2a. E.g. Bing.

Scales were not considered important by the toy makers. Appearance was all important and most makers produced models which did for several gauges with different wheel spacing’s. Usually the model in any gauge became the basis of a cheap range for the next gauge up. Scale models were still a long way off!

In 1912, Lionel in the United States began production of a range of trains using Maerklin’s philosophy of offering a complete range of trains, track and accessories and adopted the No.2 gauge. However they assumed that the 2 1/8″ gauge stated in Maerklin’s literature was measured between the rails, which was the norm in the USA. When the mistake was realized, Lionel coined the term “Standard Gauge” which is still in use today in the USA.

Around 1900, No.0 gauge was introduced by Maerklin to allow train sets to be accommodated in the smaller houses which were then being built, or perhaps it was because toy trains were becoming cheap enough to be available to people on lower incomes. The larger gauges had already fallen out of favor. Little had been produced in No.5 gauge, No.4 attracted a few one-off orders and No.3 gauge was purchased only by the very rich. No.1 being the most popular showed the need for smaller gauges. No.0 gauge immediately became popular as the price made railways accessible to the middle classes. This movement to smaller gauges encouraged makers to introduce smaller non-standard trains before WWI but none were persevered with. Was this because they were non-standard sizes?

After WW I Maerklin introduced a No.00 gauge of about 7/8″ (22mm?) This was produced from 1921 but was dropped after 3 years production. Bing of Nurnberg introduced their “Table-top” range in 1921 which was to 5/8″ gauge (between the rails), chosen because it was half No.0 gauge. This was taken up by Henry Greenly for the English market in 1923. Another German firm, Distler, produced 5/8″ gauge from 1920, but this seems to have faded away without success.

Gauges larger than No.1 did not reappear after WWI. with few exceptions. Even Gauge No.1 had faded away by the 1930’s. S Gauge made its appearance in the USA during the inter war period, notably from American Flyer. The track gauge of 7/8″ is the same as the 22mm gauge produced with little success by some European manufacturers.

Bing’s Table-top railway was “the” big success in Germany, England and even the USA. Copies were produced by various firms through-out Europe. E.g. Bub, Paya, JEP. Etc.

ZO Gauge (24mm) was a European scale to fit between O and HO. The first manufacturer was the Czechoslovakian firm Lastra, with a selection in 1938. The scale reappeared post-war from Malmo-Bahn (Werner Mahlow, Berlin) in 1949, and BeCo-Bahn (Bergmann & Co, Berlin) in 1950. The ranges were gone by the mid 1950s. Trains were becoming more true to prototype in the larger scales and individual makers used the toy gauges as a basis for producing models to scale. The actual scales used with each gauge varied, most makers rounding scales up or down which has resulted in some very odd combinations, some of which continue today.

The mid 1930s saw new ranges being introduced in OO/HO scale by Maerklin, Trix, Hornby, Lionel and others. I have deliberately used the OO/HO- scale term here as OO and HO had not settled at their present meanings except in the USA, where OO meant 19mm gauge, 4mm/1ft scale and HO meant 5/8″ gauge with 1/8″:1ft or 3.5mm:1ft. In England and Europe competitors used opposing terms, probably to keep their customers faithful to one brand.

After WW2, HP Products in the USA introduced a small range of models in TT scale. Several manufacturers in Europe followed suit and the scale had a period of popularity through the 1950s. The scale has remained popular in Eastern Europe, perhaps due to smaller homes, and in particular, due to a good range of models being available.

O scale reappeared after WWII but did not regain its popularity. The gauge remained in the toy market in Europe until about 1950, Britain until about 1960 and in the USA, Lionel faltered on until the nostalgia movement brought increased sales.

N scale began a faltering start in the mid 1950s, with push-along toys from MiniTrix and Lone Star. Arnold brought out powered models around 1960. I am not sure which of the three was first with operating models. This scale is now the second most popular, after HO.

In 1972, Maerklin introduced “Z” scale as the smallest practical size. Other firms have products in Z scale, but none provide a complete range of rolling stock and track work. Due to the precision manufacturing required, and the practical problems of dust and dirt with such tiny mechanisms, it is unlikely that any major company will bring out a smaller scale in the foreseeable future.

The 1980s and 1990s have seen a revival of larger scales. Lehmann of Germany introduced a range of narrow gauge “Garten” or “G” scale models, (No.II scale) to run on Gauge I (45mm) track. Pola followed with O scale models while Maerklin tried O scale narrow gauge on HO track. Neither range was a success. Maerklin followed with accurate scale No.I models which more recently has split into two ranges: the scale models, and the “Maxi” tinplate models for the toy and nostalgic market.

Model Railway Scales & Gauges

ScaleRatiomm/ftin/ftGauge mmGauge inNotes
Z1:2201.4 6  
N1:1601.9 9  
N(B)1:1482.1 9  
OOO1:1522 9.5 1
TT1:1202.5 12  
TT(B)1:1023 12 2
TT(C)1:1003 13 3
HO(C)1:903.4 16.5 4
HO1:87.13.5 16.5  
HO(C)1:853.6 16.5 5
HO(C)1:823.7 16.5 6
OO(B)1:76.24 16.5  
EM(B)1:76.24 18  
P4(B)1:76.24 18.8 7
OO(A)1:76.24 19  
Q(A)1:486.41/430.21 3/16 
O(A)1:486.41/431.71 1/4 
O(C)1:456.8 32 8
O17(A)1:456.817/6431.71 1/4 
O1:43.57 32 8
1(A)1:329.53/844.51 3/4 
1(B)1:329.5 45  
1(C)1:30.510 45  

The table above deals with models of Standard Gauge trains i.e. models of trains that run on 1435mm (4′-8 1/2″) gauge tracks. (A) means North America; (B) Britain; (C) Continental Europe, and the most popular commercial gauges are shown highlighted. Some of the others are uncommon but may turn up when dealing with second hand or collectors items.


  1. Has largely been supplanted by N
  2. Also known as TT3
  3. Used by Swiss firm of Wesa
  4. Was used by Trix Express in the 1960s
  5. Used by Fleischmann for European Models
  6. Was used by Fleischmann and Rivarossi in the 1960s
  7. Also called Protofour
  8. 1:45 is a standard scale on the continent but 1:43.5 is also used in France, as well as Britain.

Of the scales in the OO/HO family, only HO with a scale of 1:87.1 is strictly correct for 16.5mm gauge track. The other scales in the family are hybrids and have mostly come about due to technical limitations e.g. the size of the available electric motors at the time they were developed.