"Scale" refers to the relationship of the size of the model to the original. "Gauge" is the width of the space between the rails. In the UK, where they do nearly everything differently, the usage of these terms are actually reversed. This article deals with scales that originated in the United Kingdom, and the gauges commonly associated with them. They are still modeled there in the UK more than in other places around the world. In order for this information to be meaningful, you need to already be familiar with the common
scales and gauges modeled in other parts of the world.
UK Scale and Gauge Standards
The American NMRA and the European NEM standards define the letter designations for the various scales and gauges. All of the common letter based standards are in use throughout the UK. But the British also have their own variations on these standard letter scales. Interestingly, the British don't use the letter to designate the scale; they use it to refer to the gauge. These British scales variations are all metric, and expressed in millimetres per foot. No... that's not a typo; that's how they spell millimeters in the UK.
Confusing? Maybe for model railroaders in North America, like myself. But it doesn't seem to bother our British cousins across the pond much.At 7mm to the foot the actual scale is 1:43.5, although some British manufacturers make their products 1:45. This is slightly different from the American and European standards for O scale, 1:48. However, look at that British standard for O closely; 1/87th is exactly one-half the size 1/43.5. If you'd read elsewhere that HO stood for "Half O" then this explains it. HO apparently was based on one-half the UK variant of O scale. The NMRA and NEM standards for O scale come from the fact that O scale, originally called zero scale, was introduced by Marklin. Prior to introducing O scale trains, Marklin made doll houses in 1:48 scale.
5mm Scale / S Gauge (1:60.1)
This is a scale that never actually happened. It was proposed as a One-Half One scale, One scale being an early large scale standard. The
History and Developments page of the S Scale Model Railway Society (formed in 1946) makes mention of modelers proposing a 5mm scale around 1935. But the standards which that society adopted are those of the S scale manufactured in the United States. However, this is on case where the common letter seems to be used to identify the scale in the UK as well as the gauge, as witnessed by the name of the society.
If you read the
Scales and Gauges page, you know that OO is the most popular scale/gauge in the UK. When HO was introduced, they didn't take into account that British locomotives are usually narrower than American and European ones. At this point in our technological development, this meant that accurate scale models were too narrow for the electric motors used in HO locomotives. At the time, these were the smallest electric motors available. The millimetre scale of HO is 3.5mm to the foot. To make locomotives that the motors would fit into, they created a slightly larger scale; 4mm to the foot and called the gauge OO. At least, that's how some UK modellers tell it.
European and American TT scale is 1:120, and runs on 12mm gauge track. The 12mm TT gauge in the UK is used with models constructed at 3mm to the foot. The actual proportion works out to 1:101, and this scale is frequently referred to as "British TT".
N scale derives its letter from the fact that its rails are gauged at 9mm. European and American N scale is 1:160 scale. This same 9mm gauge track in the UK is referred to as N gauge, and is used with models scaled 2mm to the foot, or 1:148 scale.
An American's Perspective
This article is based on my web research. I do not claim to be an expert on UK scales and gauges. I wrote this article as an overview for people outside of the UK who are unfamiliar with these UK standards. I invite knowledgeable individuals to post any comments or corrections for this article in our
forum.
