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Scale vs gauge: Not quite interchangeable

Wondering about scale vs gauge? You’re not alone. It’s a common question, and I’ll try to provide a simple answer. The two terms may appear interchangeable, but they aren’t quite.

Gauge is the distance between the two rails, or the outer rails if you’re talking 3-rail track. Scale is the size of the model relative to the real thing, or prototype.


scale vs gauge: AF 561 vs Lionel 675

This American Flyer 561 (left) and Lionel 675 are both Pennsylvania RR K5s and both run on O gauge track. They are the same gauge but clearly not the same scale.

For decades, manufacturers sold toy trains based on their gauge. #5 gauge trains, the largest size, were huge. #1 gauge trains, the smallest size, were less huge. But by modern standards, they were still huge. Later they figured out how to make a smaller train. They called that 0 gauge, since they needed a number smaller than 1. Today we call it O gauge. The most popular brand name we associate with O gauge is Lionel. By modern standards, Lionels are big trains.

Nobody really talked much about scale. Size varied from product line to product line. Cheap trains were small. Expensive trains were bigger. Some had realistic proportions and some just looked fanciful.

The emergence of scale

By the 1930s, railroad enthusiasts wanted scale models of the trains they enjoyed studying. Some used existing toy-train track gauges but many of them went for a new standard called H0 or HO. The track was about half as wide as O gauge track, so “HO” stood for “Half-O.” But the main thing they were interested in was scale.  The track was about 1/87 the size of real track, so they built models 1/87 the size of the real thing to run on it. And they built model buildings 1/87 the size of the real thing to give their trains businesses to service.

Gauge can vary within a scale. In the real world, not all track is the standard 4’8.5″ wide, and models of these narrow gauge trains exist. On3 and On30 are both O scale, but they are different gauges.

Common scales and gauges

There are seven common scales and gauges you are likely to encounter today. We won’t concern ourselves further with narrow gauge, as that’s a niche.

If you’re interested in gauges of the past, #2 gauge, which was two inches wide, was popular around the turn of the 20th century, and Lionel’s nonstandard “Standard Gauge,” which was 1/8 of an inch wider, was popular from the end of World War I until the Great Depression. But both are pretty obscure today.

If you need to convert between any of the popular scales, I have a scale conversion chart.


G is the old #1 gauge that’s been around more than a century. Many different companies make or made trains this size, but it’s confusing because the actual scale varies from 1:32 to 1:22. Famous brands include LGB and Aristo-Craft.

Due to their size, outdoor G gauge layouts are popular.

LGB and Aristo-Craft had tremendous success with G gauge trains in the 1980s and 1990s but that popularity has faded a bit in recent years. It’s not as popular as O scale/O gauge anymore. Inexpensive plastic G gauge sets, often battery operated, are pretty common around the holidays.


“Proper” O scale is 1:48 in North America, 1:43 in the UK, and 1:45 in the rest of Europe. Confused? Based on the track dimensions, 1:45 would be correct, but 1:48 and 1:43 are more convenient to measure and model, since they are 1/4 inch to the foot or 7 millimeters to the foot, respectively.

Making things more confusing, many inexpensive trains for O gauge track are smaller than O scale. Lionel’s expensive trains are full O scale, but the $249 starter sets you can buy at retail during the holidays tend to be smaller than scale.

The most famous brand of O gauge and O scale trains is Lionel, although there are others. Many O scale trains use less-than-realistic 3-rail track, but 2-rail O also exists.

Although not as popular as it was in the 1950s, O scale is the third most popular scale, behind HO and N.


S scale is 1:64 scale, like popular die-cast cars. American Flyer trains, popular in the 1950s and 1960s, are this size and gauge. S scale still has a devoted cult following today but it never overtook Lionel in popularity.


HO scale is 1:87 scale. It’s the most popular scale for model railroading. It started becoming popular in the late 1950s, and its popularity grew from there while Lionel and American Flyer struggled. There are many brands of HO scale trains, and it’s often possible to find a starter set for under $150 or even under $100.


N scale is 1:160 scale, not exactly half the size as HO scale but significantly smaller. It emerged in the 1960s and now is the second most popular scale for model railroading. Like HO scale, there are many brands, and starter sets are easy to find for around $100.


Z scale is 1:220 scale, even smaller than N. It emerged in the 1970s, and its most popular brand is Märklin. Although it’s no longer the smallest commercially available scale, it can still rightfully claim to be the smallest popular scale.


T scale is the smallest commercially available scale, at 1:450. It’s less than half the size of Z scale. T scale is a fairly recent development, dating to 2006, and available models are mostly German and Japanese prototypes.

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