Scales and Gauges

It has been a while since I created a post aimed towards beginner modelers.  I myself a somewhere between a beginner and an experienced modeler.  I haven't seen everything, but I have seen a lot and part of this blog's purpose is to assist those who are just beginning with model trains with helpful information and links.  Come to think of it, I haven't done a big post on the topic of Scale and Gauge just yet.  Well, there's a first time for everything.

Scale refers to a ratio or fraction of one unit on the model equaling a certain number of units on the prototype (real life) trains.  For instance, HO scale is 1:87  meaning that one inch measured on the model represents 87 inches on the prototype.

Gauge (gage) refers to the width between the rails.  This is a fundamental difference between scale and gauge.  G gauge refers to track that is 45mm (about 1 and 7/8 inch) apart.  G scale, if there is such a thing, would refer to 1:22.5 or 1:24 scale model trains.  F scale is 1:20.3, but F scale typically runs on G gauge track, representing 3 ft gauge in 1:20.3.

Confusing?  Not to worry, while the definitions may be different, the terms are used interchangeably, even by the most experienced of modelers.  What is more important is that you the reader understand the different scales and the gauges related to each scale.  Below is a list of the different scales found in the US:

• Z scale (1:220)
• N scale (about 1:160)
• TT scale (1:120)
• HO scale (1:87 or 1:87.1)
• S scale (1:64)
• O27 scale (about 1:50)
• O scale (1:48 but some vehicles are 1:43)
• Large Scale ( can be 1:32, 1:29, 1:25, 1:24, 1:22.5, 1:20.3, 1:18, or even 1:13.7)

Now let's look at the different gauges within the US:

• 6 mm (about 1/4")
• 9 mm (about 1/3")
• 16.5 mm (about 5/8")
• 22.4 mm (about 7/8")
• 32 mm (about 1 and 1/4")
• 45 mm (about 1 and 7/8")

We will first look at Z through O and their respective standard gauges.  Standard gauge refers to a gauge that is 4 foot and 8.5 inches between the rails.  each modeled scale has their own standard gauge.  Z is 6mm, N is 9mm, HO is 16.5mm, S is 22.4mm, and O is 32mm.  However, not all trains in real life were standard gauge.  Some railroads ran on a wider gauge than standard, but many were narrow gauge.  So below is a list of different gauges found within each scale:

• Z scale only uses 6mm track
• N scale will use 9mm for standard, and 6mm representing 3 foot gauge.
• HO scale uses 16.5mm for standard, 9mm for 3 ft gauge
• S scale uses 22.4mm for standard, 16.5mm for 3 ft gauge
• O scale uses 32mm for standard, 16.5mm for 30 inch gauge and slightly wider for 3 foot gauge and 9 mm for 18 inch and 20 inch gauge.

In these smaller scales the suffix "n" is used to represent narrow gauge, followed by the prototype gauge.  So On30 means O scale narrow gauge representing 30 inch gauge.  HOn3 means HO scale narrow gauge representing 3 foot gauge.

However, this is completely different for large scale.  Large scale, instead of having multiple gauges for one scale, instead has multiple scales for one gauge.  All large scale trains run on 45mm track, known as gauge 1.  But each scale represents a different gauge:

• 1:32 (true standard gauge)
• 1:29 (slightly over-sized standard gauge)
• 1:24 (42" gauge)
• 1:22.5 (meter gauge (39"))
• 1:20.3 (3 foot gauge)
• 1:16 (30 inch gauge)
• 1:13.7 (2 foot gauge)

Again, all large scale trains run on 45 mm track.  The downside is that multiple gauges cannot be represented easily on one layout.  So for someone going into large scale, keep in mind that it would be wise to stick with one or two scales rather than having multiple scales that look incompatible. 

Of course, there are exceptions to this.  In reality, it is what looks good, not what is accurate.  In other words, "What ever floats your boat" is the mentality I take to the hobby.

Confusing now?  Let me blow your mind further.  These are just the US scales and US gauges,  There are plenty of other gauges and scales.  The next most formal is UK scales, which are similar to US scales.  The main difference is that in the UK, instead of letters, measurements are used in the metric system to represent scale while letter combinations represent gauge.  This is different than the US, which uses letters for scale and measurements for gauge.  Below is a list of formal British scales and their respective US counterparts:

• 2mm to the foot (2mm) N scale
• 3mm to the foot (3mm) TT scale which is slightly smaller than HO scale.
• 3.5mm to the foot (3.5mm) HO scale
• 4mm to the foot (4mm) OO scale which is slightly larger than HO scale but runs on the same track.  There are also several types of 4mm scale trains.
• 7mm to the foot (7mm) O scale.  Again, there are different types of this scale as well.
• 10mm to the foot (10mm) G scale or gauge 1.

 4mm and 7mm scale trains have different gauges used to represent standard, true standard, and various narrow gauge prototypes. Below is a list of different 4mm gauges:

• HO gauge (16.5mm gauge track with a scale of 1:87)
• OO gauge (16.5mm gauge track with a scale of 1:76)
• EM gauge (18.3mm gauge track with a scale of 1:76)
• P4 and S4 (18.8mm gauge track with a scale of 1:76 representing true standard gauge)
• OO9 gauge (9mm gauge track with a scale of 1:76 representing narrow gauge)
• OOn3 gauge (12mm gauge track with a scale of 1:76 representing 3 ft narrow gauge)

And the 7mm gauges:

• O gauge (32mm gauge track with a scale of 1:43)
• Scale 7 (32mm gauge track with a scale of 1:43, but the track is a more accurate model)
• 16.5 gauge (16.5 gauge track with a scale of 1:43 representing narrow gauge)

Finally, there are several universal gauges which have been used in the past, all representing standard gauge:

• Gauge 0 (32mm gauge track)
• Gauge 1 (45mm gauge track)
• Gauge 2 (63mm gauge track)
• Gauge 3 (89mm gauge track)
• Gauge 5 (127mm gauge track)
• Gauge 7 (184mm gauge track)
• Gauge 10 (260mm gauge track)

Gauge 5 and up are commonly known as "riding scales" since the trains are big enough to be ridden.

Now are you confused?  Well, there is one last thing I want to show you then. Below is a list which I don't think has been made before.  This list shows all the scales and all the gauges used by the different scales.  The scale goes from largest to smallest Z through gauge 10.  Within each scale I will have listed the various gauges used starting with the narrowest gauge and ending with standard gauge.  This is my best attempt so far at a complete listing of all scales and gauges in order of least to greatest:

• Z (1:220)
• Nn2 (1:160)
• Nn3 (1:160)
• N (1:160 US 1:148 UK)
• TT (1:120)
• HOn2 (1:87)
• HOn3 (1:87)
• HO (1:87)
• OO (1:76)
• EM (1:76)
• P4 (1:76)
• Sn3 (1:64)
• S (1:64)
• On2 (1:48)
• On30 (1:48)
• On3 (1:48)
• O (1:48 US 1:43 UK)
• O14 (1:43)
• O7mm (1:43)
• Scale 7 (1:43)
• Mn2 (1:35)
• Mn3 (1:35)
• M scale (1:35)
• #1n3 (1:32)
• Gauge 1 (1:32)
• Gnine (1:24)
• Gn15 (1:24)
• Gn18 (1:24)
• G scale (1:29 - 1:24)
• Gauge 2 (1:22.5)
• Fn3 (1:20.3)
• F (1:20.3)
• Gauge 3 (1:16)
• 7/8" scale (1:13.7)
• 1" scale (1:12)
• Gauge 5 (1:11)
• Gauge 7 (1:8)
• Gauge 10 (1:5.5)