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Choosing a Model Railroad Scale & Gauge


Many modellers are unaware of the importance of Scale when they receive or purchase their first model train set, yet, ultimately one of the most important decision that a model railroad enthusiast has to make concerns scale.
Let’s clarify the terms SCALE and GAUGE which are commonly mixed up, but actually have very different meaning.
Refers to a models relative size as compared to the real thing
(or in other words: the ratio of the model compared to the full size item)
There are several Standard Scales in the world of model railroads, and there is no right or wrong when choosing a scale, although there are definite advantages (as well as a few disadvantages) to each.
Refers to the measurement between the rails of a railway track.
Technically there is no such thing as HO gauge – It is HO scale.
In reality you will often see terms like HO gauge, N gauge etc. Manufacturers don’t see this as “wrong”, just a little less accurate..
One example of why we would use a different Gauge is commonly found in HO, where a HO model may run on different gauge tracks. For example if modelling a narrow gauge railway, the track will be smaller, but the scale will be the same.
 Additional Resources that forms part of this Series:




So where to start ?

Here are some fundamental Considerations to Make when Choosing a Model Railroad Scale:

  • Cost
    For most people, cost is a major consideration when selecting a scale for a model railroad. It’s important to choose a scale that has accessories and pieces that fit within the available budget. Look up prices for model railroad accessories in several different scales to get a feel for how much each scale typically costs.
  • Popularity
    The more popular a model railroad scale is, the easier it will be to find accessories, engines, and rolling stock for it. With less popular scales, it’s often necessary to build pieces from scratch. Those who don’t enjoy building from scratch should stick with more popular scales. More popular scales also tend to be a lot more affordable, which makes it easier to create more elaborate layouts.
  • Available Space
    The amount of space that is available is a very practical concern. If plenty of space is available, a broader array of scales can be considered. If space is limited, however, it is generally best to stick with smaller scales. Be realistic when considering the amount of space that is available. If furniture needs to be moved and other concessions need to be made, it may not be worth it.
  • Minimum Curve
    Another way to determine whether there’s enough space for a particular scale is by considering minimum curve. Minimum curve refers to the smallest curve that a model railroad train can make without derailing. A good way to determine this is by considering the smallest section of track that is available. To achieve a nice layout, it’s generally necessary to have at least one 180-degree curve. Different scales have different minimum curves, so keep this point in mind.
  • Eyesight
    Building and using a model railroad is a lot more enjoyable when it’s easy to read the writing on the engines and rolling stock. Some people don’t mind having to use magnifying glasses, but others would rather not have to do that. There are several scales, including HO and N, that offer a nice compromise in this regard.
  • Local Clubs
    When space at home is extremely limited, joining a local model railroad club is a good way to make the most of the hobby. These clubs consist of enthusiasts who have a large space where they set up their model railroads. Find out which scales the local clubs use before selecting one. Otherwise, it may be impossible to participate with local clubs.
  • Desired Layout
    Before laying a single piece of track, many people have pictures in their minds about how their model railroads will be laid out. Some scales are more conducive to certain layouts than others. The desired level of detail should be kept in mind too. Some scales make it easy to add a lot of detail while others are decidedly limited.
  • Children
    If children are going to join in on the model railroad fun, it’s important to keep their small hands in mind. Extremely small scales have pieces that may be difficult for little hands to manipulate. This may also be true about elderly people who have a hard time managing very small objects. Also, larger scales tend to be more durable, so they are less likely to be damaged or destroyed by clumsy hands.

Now that you are aware of some fundamental considerations, here is a General overview of the Popular Model Railroad Scales:





HO Probably the most popular model train scale, HO equals a scale of 1:87. It is larger than the N scale, which is also quite popular, but it can be used to create very realistic layouts without having to use more space.

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.

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.  HO trains run on a 16.5mm gauge track.

  • It’s easy to find accessories and features that are designed for the HO scale
  • HO accessories tend to be very affordable
  • May be a little too small for very young children to handle effectively
  • Requires a little more space than the N scale, so it may not be suitable for people who have very limited amounts of space.
OO 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 not as tall or wide as those of many other standard gauge railway systems. Therefore there was difficulty fitting the bulky motors of the time into 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 manufacturers 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 gauge. EM stands for Eighteen Millimetres. This is a specialist scale not commonly seen in Australia.
Taking this gauge accuracy to further extremes, there are some modellers who choose to reduce all dimensions exactly to 1:76 scale, particularly wheel flanges and flangeways at turnouts. This is known as P4 (ProtoFour). Track gauge is around 18.83

Most manufacturers of OO scale will fudge a little on the gauge so that the locomotives and rolling stock will run on HO track

  • It’s easy to find accessories and features that are designed for the HO scale
  • HO accessories tend to be very affordable
  • May be a little too small for very young children to handle effectively
  • Requires a little more space than the N scale, so it may not be suitable for people who have very limited amounts of space.
N With a scale of 1:160, N scale is the second most popular option among model railroad enthusiasts. According to various Model Railroad Manufacturer sales-surveys, N-SCALE is the fast becoming more popular.

The models are nearly half the size of HO / OO and as a result you can get much more 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

  • Offers a nice compromise that allows people to create very realistic and detailed layouts with limited amounts of space
  • Gradual curves are possible, which makes this scale much more versatile
  • Although there aren’t quite as many N accessories as O accessories, new options are made available all the time. As N scale becomes more popular, more options should become available.
  • The smaller size of N scale trains and accessories make it a less-than-optimal choice for young children and elderly enthusiasts who may have trouble working with small pieces of rolling stock
  • Fewer accessories are available, so achieving the perfect layout is more difficult
  • Prices tend to be a little higher for N-scale trains and accessories
OOO 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.

Most OOO gauge was from Lone Star Locos which was a range of die-cast push-along trains made in the UK

They ran on metal track closer to 8.5mm gauge. Later some electrically powered models were made, but they are relatively rare today

O With a scale of 1:48, O-scale trains and accessories are quite large. Most people associate this scale with toy trains.

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).

The locomotives are big and impressive and are a favourite of young and old “kids” alike. The 2-rail version runs on DC current. The O scale trains tend to dwarf the scenery unless you have a very large room for the layout, but they sure are fun to run!

O27 Scale: This is also 1:48 scale, but the difference is in the tighter curves. (O27 track sections will make a 27″ circle compared to the standard O scale track sections which will form a 31″ circle.) Also, O27 rail is a little shorter and thinner than standard O scale. Lionel is the primary, or at least the most famous, manufacturer of O27 these days – most, if not all, produced in the 3-rail version running on AC current. Lots of accessories are available with working parts (circuses, sawmills, etc).

Another Gauge is 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, Australia is one 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.

  • The large size of this scale makes it suitable for young kids and elderly people, who have a much easier time manipulating larger pieces
  • This is a fairly popular scale, so there are plenty of accessories on the market
  • Rolling stock and engines can be enhanced so that they look very realistic because of the large size of this scale
  • On30 has many of the advantages of G scale without the serious cash outlay. You also don’t need so much space
  • A lot of space is needed in order to make an O-scale layout look realistic at all
  • The larger size of this scale means that it tends to be more expensive. It’s often necessary to spend a lot more money to complete a single layout
  • Much sharper turns are needed due to space constraints, which makes these sets look a lot less realistic and more like toys
G The G scale, or garden scale, ranges from 1:22.5 to 1:29.

Good size for running a train around a Christmas tree!

Commonly used for garden layouts. Also called LGB scale. If you like working outdoors, doing real landscaping and gardening, this is the most likely model train scale you’ll want to use.


G gauge was introduced in 1968 by Lehmann of Germany.

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.


  • Most of the pieces made in G scale are also designed to be used outdoors, which makes it easy to create a garden railroad
  • This scale’s exceptionally large size makes it suitable for very young children and for older adults who have difficulty manipulating small pieces
  • 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
  • High-quality rolling stock, engines, track, and accessories are very expensive
  • This scale isn’t nearly as standardized as other scales, as evidence by the size disparities between manufacturers
  • Pickings are slim in terms of accessories
  • A massive amount of space is needed to create a G-scale layout.
  • Not ideal if you are short on space, however, the smallest radius track is 600mm, so it can be fitted into a relatively small area considering its large scale.
  • Models seem expensive at first, but do actually represent value for money if you investigate further.
S 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.
  • 1not as popular as some of the others but definitely has a rowing as a home for a lot of followers and offspring from the American Flyer era

With a scale of 1:100 (in some countries this is 1:120) and 12 mm gauge, this Scale is only supported by a relatively small number of manufacturers.

TT Scale was superseded by N Scale 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.

Modellers use TT track and mechanisms with their HOn3½ Scale, which represents 3’6″ gauge in HO scale.

  • May be a option if space is a major issue
T T- Gauge has a scale of 1:450.

T stands for Three (3) mm gauge.

A relatively new scale for model railways (introduced in 2007 by Japanese company, K K Eishindo), it is a 2-rail electric system running on 4.5 – 5 volts with motorised trains.


  • There is a range of scenery, structures, track and all you need to construct a working model railway in a very small space
TY TY has a scale of 1:900.

Made by Tiny Trains of South Dakota, these pre-built layouts use cast metal trains attached to a belt under the ‘track’.

TY stands for “TinY”

  • May be a option if space is a major issue
  • Train consists cannot be altered
  • Turnouts are not available


Not the smallest Scale, but probably the smallest commercially supported scale.

Introduced by Marklin of Germany in 1972, it is 1:220 scale and runs on 6.5mm gauge track.

Marklin is one of only a few manufacturers to support Z Scale, although there seems to be random products available from a handful of US and Europeancompanies.


  •  Easier to transport as it may require less space
  • an entire Z scale model railroad empire can fit inside a suitcase
  • can be used effectively in the background of an N scale or HO scale layout for forced perspective so that it looks like you have trains or structures way off in the distance when viewed from eye level. This makes your HO or N scale layout look even bigger than it really is.
  • This scale is great for coffee tables, a nice addition to your executive desk
  • Also a good choice for any “large” layout in a very small space.
  •  Small size me a challenge for people who cannot see properly
  • Smaller size means less detail
  • Limited availability
  • Limited production and manufacturing means less choices and typically higher prices
  • 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.
HOn3 Narrow gauge designation indicating basically that you have HO equipment running on track that measures only 3-1/2 scale-feet between the rails instead of the usual 4ft 8-1/2in.

The prototypes for narrow gauge railways are usually logging railroads where sharp turns around rocky, mountainous terrain are required.

While there are modellers out there that will defend their preferred Scale(s), the fact remains that there is no single scale that is perfect for everyone. That said, the three most popular scales are:

  • HO/OO Scale
  • N Scale
  • G Scale

Many people cannot decide between an HO-scale and a N-scale model railroad, and my advise is to make your decision by considering the following additional criteria:-

  • Space
  • Detail

Here are some ideas:

  • If you have Space constraints:  N-Scale is the best choice
  • If you have plenty of space, and want to it in so much more: N-Scale is the best choice
  • In General HO Scale offers more detail
    (e.g: face expressions on N-Scale figures are hard to see, fruit and vegetables may be just blobs of color)
  • If you cannot work delicately, and want to build your own models:  HO is probably for you
  • If your eyesight is a problem: HO is your best choice
  • If you are going to inherit HO.. stick to HO
  • For Garden railroads go with G-Scale
  • HO and N Scale are most widely available in local hobby shops, but sometimes HO is the only option- The Internet has made ordering products from any scale much more accessible, so this should not really be an issue anymore


  • One way to zero in on the right scale for a model railroad is by considering the most popular options.
  • While there are a few obscure scales out there, they only tend to appeal to very limited groups of people.
  • The most popular model railroad scales offer the most versatility, and they tend to be the most affordable too.
  • Due to the history of the hobby, you will notice a mix of metric and imperial measurements are used in magazines and even by the manufacturers.


  • By weighing the pros and cons of various model railroad scales you can easily find the option that is right for you.
  • Going back and switching scales later isn’t practical, so it pays to think things through and to consider as many points as possible.

After choosing a specific scale, the real fun begins.. Start Here

Article Credit:  various

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