What are the Different Model Train Scales and Gauges?

Though model train sets can be as big or as small as you want, especially if you decide to the take the construction of the surrounding landscape upon yourself, there are generally some rules that are followed for the sizing and manufacturing of most model train sets on the market today. Any popular or renowned model train exhibition in the world is always built to a standard code that it lists among its specifications.

Two of the most commonly used terms to describe the sizing of model train sets are ‘scale’ and ‘gauge’. Sometimes, these terms are used interchangeably with each other, but they actually mean completely different things. This will be a brief summary of the two terms; just enough to give you an idea of what the different denominations mean and help you get started on understanding the world of model trains a bit better.

The Difference Between Scales and Gauges

For starters, let’s first discuss what both terms actually mean. As mentioned above, though confused with each other quite often, scales and gauges could not be more different. The gauge, when referring to a model train set, is simply the measurement of the distance between the outer rails of the model track that is being used. The scale on the other hand, is a ratio measurement comparing the model train to the real life equivalent. The parameters of allowed gauges thus, do depend on the scale the model is being built to.

When Were Both These Terms First Coined?

As model railways started to gain popularity amongst hobbyists during the 20th Century, model train set manufacturers decided to standardize the different sized products they were producing. This is when the term ‘gauge’ was first introduced. Gauges weren’t new sizes; instead, they simply conformed to the already existing scales the model trains were being produced at.

At the time, four different gauge sizes were introduced. These were Gauge O (with a scale of ¼ inches to 1 foot), Gauge 1 (with a scale of 3/8 inches to 1 foot), Gauge 2 (with a scale of 7/16 inches to 1 foot), and Gauge 3 (with a scale of 12/32 inches to 1 foot). Other gauge sizes were also introduced, but the above four were the ones that covered the most popular scales of model train sets back in the day.

The origin of the term ‘scale’ cannot really be traced back to any definitive point. It was just a given that model trains would be measured to their real life equivalents and assigned a scale based on the results of that measurement. However, we can be positive that the term ‘scale’ existed before the term ‘gauge’, because ‘gauge’ was literally coined to cover popular scales.

What are the Popular Scales in Today’s Model Trains?

The 20th Century saw multiple new scales being introduced to the model train community. Some scales came about because manufacturers wanted to portray their models as accurately as possible relative to their real life equivalents. Other scales came about as houses began to shrink in size and manufacturers had to respond by building even smaller model train sets so the market could continue to thrive under the changing circumstances.

The smallest model trains you could get yourself today are made according to the ‘Z Scale’. With a track gauge measuring a very tiny 6mm, Z Scale model trains are built to 1:220 measurements. This has allowed very large and condensed recreations of real life train stations and adjacent towns and cities to be built in relatively cramped spaces. Slightly larger than the Z Scale is the N Scale. With a track gauge of only 9mm, the scale measures up to 1:160 and allows for slightly larger model train sets that can still be constructed inside small areas.

Then comes the scale that is the most popular among model train hobbyists the world over. Named the HO Scale, this scaling standard is exactly half the size of the Gauge O mentioned above. The track gauge in the HO Scale measures 16.5mm, and the ratio measurement comes out to 1:87. The HO Scale was devised by German model train set manufacturers shortly before World War 2, and is the most sold scale today because of its neat balance between being compact and still being large enough to allow for exquisite detailing.

Then comes the S Scale of model train sets. This scale is only slightly smaller compared to the O Scale, and has a track gauge measurement of 22.43mm with a ratio measuring of 1:64. The S Scale was first used for toy trains, but has since become known for its extremely detailed model train sets that mimic their real life equivalents down to the smallest detail. Then we arrive at the O Scale. The O Scale is officially part of the “big model train” category; it has a track gauge measurement of 30mm and a ratio measurement of 1:48 (though the gauge and ratio measurements may slightly differ depending on manufacturer and region).

Finally, we come to the largest scaled model train sets that are produced nowadays. These models can range from a ratio of 1:32 to a ratio of 1:20. Called the ‘G Scale’, these model train sets, though capable of being used indoors if needed, are popular among model train hobbyists that wish to recreate train set outdoors in their backyards or someplace similar.

Less Popular or Discontinued Scales and Gauges

The above-mentioned scales are all popular model train set scales and gauges that are produced and readily available today. However, there have been, or still are, other measurements as well. Some gauges are insanely large and can be either 3.5 inches, 5 and a half inches, and 7 and a quarter inches. These sizes are normally considered too large to be called model trains however, and instead get promoted to the category of miniature live trains.

There is also the OO Scale. It uses the same track gauge measurement of the HO Scale but its ratio measurement is 1:76 instead. There is also an Eighteen Millimeter Society, an organization that devised a scale of 4mm:1ft to remain true to real life scaling of trains. After a while, some people thought this was too extreme, and founded the Protofour Society. Also known as the P4 Society, this organization adopted a track gauge of 18.83mm. This society was also superseded by the Scalefour Society, who brought the track gauge measurement down to 4mm. Another scale that never received much attention from the consumers was the TT Scale. Table-Top Scale as it was called, it had a track gauge measurement of 12mm and a ratio measurement of 1:101.6.


And that pretty much covers all the model train gauges and scales that ever saw the light of day. Some died out, some went on to conquer the world, and others still managed to form niche followings around them. Which scale or gauge should you go for? That is something only you can answer after carefully evaluating how much space you have to work with, how much budget you’re willing to spend, and what kind of model train set pieces you wish to create and how much time you will actually devote to this hobby.