Visual Guide to Railway Gauges

Track gauge; the width between load-bearing rails, arguably defines any given railway. Though it is largely standardized in many parts of the world, variations in gauge see all sorts of different railways running separately to one another and represent changes in requirements for routes across all sorts of settings. Gauge is also crucial in the modeling world and one of the most important decisions a modeler will make is choosing which scale to model in, which determines what gauge of track will be used. Below we take a simple look at some of the most popular gauges, from the smallest model railways, up to the largest 'real' railways in the world.

It is important to note that gauge and scale are totally separate things. Gauge (as defined above) is relevant to all railways, model or not, whereas scale ratio represents the proportion that a model item is of the original. In railway terms, the full-scale gauge of track recreated by a certain modeling scale is referred to as the 'prototype'.

• T Gauge: Despite offering the smallest scale for railway modeling, T Gauge is actually a recent addition to the modeling world, having been introduced in 2006. The 'T' stands for 'Three-millimeter' as the track gauge in just 3mm in width, making detail hard to replicate at times and the rolling stock incredible fragile.
• Z Gauge: At 6.5mm, Z gauge is over double the width of 'T' but still one of the smallest commercially available modeling scales. It is manufactured more widely and most notably by German maker Märklin, who introduced it in back in 1972. Due to both its popularity and size, Z gauge makes its way into all kinds of settings, including the 'briefcase layout' which can be packed up and made portable for easy transport to exhibitions, model railway clubs and other people's homes.
• N Gauge: At N gauge, things start to get complicated and the importance of distinguishing gauge from scale becomes crucial. N gauge track is 9mm in width, but depending on which nation you are modeling in, the scale can alter. In most parts of the world, including the USA, the N scale is 1:160 meaning that a model locomotive is 1/160th the size of the real thing. But in the UK, the scale is 1:148. In addition, a number of other scales use the 9mm track width, including OO9, which is popular for layouts recreating narrow gauge British railways, such as those in Wales or the Lynton & Barnstaple Railway in North Devon. One of the largest layouts in US N scale is at the San Diego Model Railroad Museum, which would be approx 33 miles long if recreated in 1:1 scale.
• OO / HO: OO and HO scales are the most popular scales of modeling in the UK (OO) and the rest of the world (HO) respectively. In order to model standard gauge track at 4 ft 8 1/2 inches, these scales both use 16.5mm track, which is widely produced by a number of high profile manufacturers such as Hornby and PECO. However, despite modeling the same gauge of prototype track, OO and HO use slightly different scaling with OO using 1:76.2 and HO 1:87. This makes the British OO an incorrect scale, represented by what is called a 'gauge error' of 12.4%. Both OO and HO have histories going back as far as the 1920s and with an entire industry build around 16.5mm track, remain highly popular with new modelers in the UK and the world over.
• O Gauge: At approximately double the width of OO or HO track, O gauge might initially seem to be better for modelers looking to recreate high levels of detail in their layouts and rolling stock. However, this was not necessarily the aim when the gauge of 30-33mm first appeared in the 1920s. Back then, these larger models were marketed very much as toys and not for the adult market. As a result, rolling stock could be cumbersome and durable, rather than delicate and detailed, to allow for ease of use by a younger audience. Since then, O gauge has grown to appeal to modelers who prefer to see minor details on their locomotives, as the large size makes weathering, pipework and lettering much easier to recreate.
• G Gauge: At 45mm in width, G Gauge track starts to blur the line between large model railways and narrow gauge passenger-bearing railways. This is because unlike smaller gauge model layouts, G Gauge layouts can often be seen outdoors, having to traverse the obstacles and gradients created by garden ponds, flowerbeds and real grass lawns. A number of different scales run on this width of track to represent a variety of prototype gauges, including A, F, G and H scales.
• Rideable, Live Steam gauges: Beyond G gauge, modeling railways can become much more engaging with both the introduction of live steam (something possible, but much more difficult to achieve with smaller gauges), and the ability to ride on the trains themselves. Miniature railways and railroads that take on full sized passengers exist across the globe and can vary from personal follies and hobbies in one's back garden, to extensive layouts passing through country parks, mountain passes and around theme parks and museums. The smallest rideable gauge is often cited as 2 1/2 inch (64mm) gauge railways, with the track elevated on stilts and the driver / passengers straddling the rolling stock with legs dangling either side. Various intervals exist up to and beyond 7 1/4 inch (184mm) by which stage riding inside the locomotive and sitting inside specially-made carriages becomes possible. Popular examples are those such as the Beer Heights Light Railway - one of the longest 7 1/4 inch gauge tracks in the UK. Train Mountain, in Oregon, boasts the largest miniature railway in the world, running a slightly larger 7 1/2 inch gauge on a route that extends to 36 miles!
• Minimum Gauge: Doubling or tripling many of the Live Steam miniature gauges results in the 15-20 inch gauge (381-508mm) range seen across a multitude of private and industrial railways over the past 200 years, firstly in France and then the UK. Today, a handful of these railways remain as tourist ventures including the 18 inch Bicton Woodland Railway and 15 inch Kirklees Light Railway - both in England.
• Narrow Gauge: Narrow Gauge Railways have been used the world over due to the ability to create tighter curves along steeper gradients cheaply. From far-flung places like rural South America and mountainous regions in India and Switzerland, to established Standard Gauge countries like the UK and USA, Narrow Gauge has been employed to suit the needs of passengers, freight, mining and the military. Measuring between 600 - 1047mm, a range of different looking locomotives and rolling stock can be seen riding these lightweight, versatile tracks and today form many tourist railways or even extravagant garden layouts!
• Standard Gauge: Familiar to millions (if not billions) of railfans and rail users across the globe, Standard Gauge is that used by some of the first and more prolific builders of railways. The UK, USA, China, Australia and most of Europe use this 1435mm wide track (still defined as 4 ft 8 1/2 inches wide and therefore 1435.1mm in some places). In fact Standard Gauge is used in over half of all railway lines worldwide. It was far from the first gauge used however. George Stephenson preferred a slightly narrower gauge for his first railways (1422mm) and his son Robert reportedly admitted to wishing that Standard Gauge was a "...a few inches more...". Rumours occasionally surface that Standard Gauge was derived from Roman Horse and Cart tracks, but this has never been convincingly proven.
• Broad Gauge: Competing with Stephenson's Standard Gauge for superiority in Victorian Britain was Isambard Kingdom Brunel's Broad Gauge of 7 ft 1/4 in or 2140mm. Though Standard Gauge prevailed, with Broad Gauge being taken up entirely after 1892, elsewhere in the world the wider rails were still being laid, despite neighboring countries following Britain's lead with Standard Gauge. Iberian Gauge became the norm in Spain and Portugal at 1688mm with passengers having to change railways entirely at the French border, a gimmick today ruled out now that all new high speed rail in Spain has been built to Standard Gauge instead. As we have mentioned in a past We Are Railfans article, Broad Gauge also appears in peculiar places like San Francisco's BART system and is widely used in India, Pakistan and Sri Lanka.

When comparing the size of the minuscule T Gauge to one of the world's Broad Gauge Locomotives, the latter is over 550 times the size of the former! It is with this in mind that the visual guides have been split into three parts - smaller gauges would have been too small to see in comparison!