Knowledge > Scale Types > Scales And Gauges

Scales and Gauges

HO or OO scale.
These are by far the most common scales in use with the largest range of items available. To sort out any confusion (?) HO models are built to 1:87th scale. This simply means all the dimensions of the full size item (the 'prototype') are divided by 87. So 87 models all lined up would be the same length as the prototype. 87 stacked up would equal the height of the prototype. To put it another way. HO is also known as 3.5mm scale. 3.5mm on the model represents 1 foot (12 inches) on the prototype or full size item. HO scale actually stands for Half O. See the O scale entry for more information. HO trains run on a 16.5mm gauge track.

OO scale is generally only used for models of British prototype. It is 1:76th scale or 4mm to the foot. The trains still run on the same 16.5 mm gauge track as HO models. OO models are slightly larger than HO, but the difference is not normally noticeable. Historically, the reason for this discrepancy appears to be that HO was first introduced in Germany in the 1920's. Naturally, there was soon demand for similar sized models for the British market. Due to tighter clearances in tunnels, under bridges, in platforms etc., full size British trains are lower and narrower than those of most other countries. Therefore there was difficulty fitting the motors of the time into most British models made to HO scale. And so they were made slightly larger to overcome this problem. This also made them more visibly compatible size-wise. Although the scale was larger than HO, the 16.5mm gauge was retained for compatibility.

Today, the scale is too well established to change it. A few companies have previously tried to introduce British HO scale, but had not been successful. Some more experienced modellers, dissatisfied with the scale/gauge discrepancy of OO have replaced the 16.5mm gauge track and wheels with 18mm gauge track and wheels. This is known as EM scale (or gauge). EM stands for Eighteen Millimetres. This is a specialist scale not commonly seen in Australia.

Both HO and OO scales have by far the largest range of trains and accessories available of all the scales. Small enough to fit a reasonable amount of railway in a reasonable space, and large enough to be easily handled and seen.

N scale.
This is the next most popular scale. The models are nearly half the size of HO / OO and as a result you can fit about 4 times as much track and scenery into the same space as those scales. N is generally 1:160th scale, or 2mm to the foot. The track gauge is 9mm. N stands for Nine. Cost of N item for item is comparable with HO. But as you tend to end up with more of it over time, it can be considered slightly more expensive. However, for a small layout, you might find it is actually cheaper to work with.

Ideal when space is at a premium or if you like long trains, sweeping curves or making lots of scenery. Can be fiddly if your eyesight isn't as good as you wish it was or if you consider yourself a 'fumblefingers'.

G gauge.
Or LGB as it is often known. G gauge was introduced in 1968 by Lehmann of Germany. G scale is generally 1:22.5 scale. However, the models are produced in various scales just to confuse things, So the term G gauge tends to be used instead of G scale. It's also known as Large scale or Garden Railway. The gauge is 45mm. LGB, by the way, is a brand name. It stands for Lehmann Gross Bahn (Lehmann being the manufacturer, gross bahn being German for large railway) The models are weatherproof and look great set up in the garden.

Great for outdoor use or large rooms. Very easy to handle and generally very well constructed. If you like trains that run when they are supposed to and easy to set up, then consider G gauge. Not ideal if you are short on space. Models seem expensive at first, but do actually represent value for money if you investigate further.

On30 means the models are O scale (1:48 running on 32mm gauge track). But the 'n' signifies Narrow gauge. 30 means 30 inches, or 2.5 feet. This means the full size train runs on 2 foot, 6 inch gauge track (Puffing Billy in Victoria is a famous example of a 2.5 foot gauge railway). So the model must also run on narrower track. It just so happens that 16.5mm gauge (HO) track is an almost exact match for 30 inches in 1:48 scale, so what we have is O scale trains running on HO track. This size is gaining popularity due to Bachmann's ready to run models in On30 scale. It allows a layout that takes no more room than HO scale, but the extra size to construct more detailed models.

Has many of the advantages of G scale without the serious cash outlay. You also don't need so much space.

There are many other scales available, including:

Z scale
This is the smallest commercially supported scale. Introduced by Marklin of Germany in 1972, it is 1:220 scale and runs on 6.5mm gauge track. It is still available and a large range is manufactured by Marklin as well as a number of others in the USA and Europe. Hobbies Plus was once a stockist of this range and would consider it again if there was the demand.
Relatively expensive compared with N scale (probably the main reason it has never become as popular as N), and with a much more limited range of models available. It does not use a great deal less space than N scale.

OOO scale
This was the forerunner to N scale, being 9.5mm gauge. Virtually extinct now. The name for this scale seems to be a logical step from O, to OO and then OOO scale. In Australia, most OOO gauge was from Lone Star Locos which was a range of die-cast push-along trains made in the UK (although with some items made in Australia). They ran on metal track closer to 8.5mm gauge. Later some electrically powered models were made, but they are relatively rare today. See the photos on the History of model railways page.

TT scale
This is one of the scales considered obsolete by the trade. It is 1:100 or 1:120 scale and 12 mm gauge. Although supported by a very small number of manufacturers, it was superseded by N in the 1960's before it had much of a chance to establish itself. TT stands for Table-Top as it was an ideal size to set up on an average sized table. In Australia, most use of TT is track and mechanisms for HOn3½ which represents 3'6" gauge in HO scale.

S scale
Another virtually extinct scale in Australia. That is apart from Sn3½ narrow gauge models which use HO track to represent 3'6" railways. The scale is 1:64 and the gauge 22.22mm (an entirely non-metric scale). S stands for Seven, Sixteenths and Sixty-four. Numbers which are commonly used in this scale when not trying to use metric equivalents. S scale has a larger following in the USA where it was made by American Flyer and in the UK there is also some support for this scale.

O scale
O scale can't be considered obsolete. In fact it is regaining former popularity. The well known Hornby tinplate trains of the pre 1960's were O gauge (32mm). In the past (about 100 years ago), the model train sizes were referred to by numbers. Gauge 3, gauge 2 and gauge 1 (45mm) being the smallest. So when a smaller size was introduced, the "baby" trains were known as 0 gauge. Today 0 or O gauge is considered large and few really have the room for it inside. Models are to 1:43 (UK) to 1:48 (US). HO gets it's name from being Half O scale. In Australia, O gauge is mostly used by modellers who build trains from detailed kits or from 'scratch' (raw materials). Very little is available off the shelf in ready to run form. The case in the USA is quite different, but it is not the subject for this page.

O 27
You don't normally encounter this one in Australia, but it is very popular in the USA. This is 3-rail O gauge made by Lionel and some others. The 27 simply refers to 27" diameter curves of the track. Introduced in the days of tinplate trains, it is still produced today.

Gauge 1
Although models for this size (45mm gauge, 1:32 scale) are still made by Marklin of Germany, it has been somewhat eclipsed by G gauge, which has the same track gauge, but a larger scale.

The foregoing is by no means a complete list of all scales and gauges ever made or still available. It only covers the more common varieties that the beginner may read about. There are also many narrow gauge scale / gauge combinations. To briefly explain (?) the confusing names, I offer the following.

Narrow Gauge.

When models of narrow gauge trains are made, there are a number of methods of describing the scale and gauge combination. One popular scale / gauge combination is using HO scale models running on N gauge track. This effectively simulates trains running on 2'6" gauge track. Puffing Billy in Victoria is the most well known railway of this gauge in Australia.

To indicate this scale / gauge combination of such models, we usually say that they are HOn2½. The "HO" indicates HO scale, naturally enough. The 'n' indicates narrow gauge. "2½" means 2 and a half feet or 2 feet, 6 inches (2'6"). However, just to confuse things, in Europe the same scale / gauge is known as HOe. The OO equivalent in the UK is known as OO9. This refers to OO scale running on 9mm (N) gauge track. OO9 is generally used to represent 2 foot gauge railways. All three names effectively refer to the same thing.
Most narrow gauge modellers in Australia use the US method describing the scale, followed by 'n' and the prototype gauge in feet and inches. eg. HOn2½. British modellers instead describe the scale followed by the model track gauge in millimetres. i.e. OO9.

Here are some of the more common names and what they mean. Using this information, you should be able to work out the meanings of any other narrow gauge scale names you may come across.

HOn3. This is HO scale on track representing 3ft gauge railways. Very popular in the USA where many such lines existed. Track gauge is 10.5mm. Has a comparatively minor following in Australia.

HOn3½. HO scale on track representing 3'6" gauge tracks as used in Queensland, Western Australia, Tasmania and South Australia. This uses 12mm gauge (TT) track.

HOm. This is a European size. It is HO scale representing metre gauge railways. It uses 12mm gauge track and so is effectively the same as HOn3½.

HOb5¼. Not so common, and not narrow gauge either. However, I include this to explain that some modellers run HO models on about 18mm gauge track to represent broad gauge (5'3") trains as run in South Australia and Victoria. For those confused by imperial measurements, 3 inches is the same as a ¼ of a foot (12 inches).

Nn3. This scale uses 6.5mm gauge (Z) track in N scale. Known in the UK as N6.5

G45. Gm. This is the same as G gauge. G45 is used by Peco to describe G gauge which is 45mm gauge. Gm is simply another way to describe G gauge representing metre gauge trains.

SM 32. This is Sixteen Millimetre scale (16mm on the model equalling 1 foot on the prototype) running on 32mm gauge (0) track. This is a size not often seen in Australia, but is used by some live-steam enthusiasts.

O16.5. This is O scale on HO (16.5mm gauge) track. It is the same as On30 (O scale, "n" narrow gauge, 30 inch prototype gauge) and On2½ (O scale, "n" narrow gauge, 2½' or 2'6"). 30 inches being the same as 2 foot 6 inches. So simple, isn't it?