Please note: I wrote this article some time ago for another site that I used to own. It's not really up to TG standards as it has no images to illustrate it. This is an issue that I hope to rectify as and when I have time to take suitable photographs but in the meantime I offer it here in it's original text only format:
There seems to be quite a lot of confusion about scales, particularly amongst those new to model making, but also among a good number of the 'old hands' who've simply worked around them without ever getting to grips with what they really mean. In fact the basic concepts are not difficult to understand and much of the confusion comes about as a result of the various ways in which scales are expressed.
I doubt that there's anybody out there who would have difficulty understanding what I meant if I referred to something as being 'quarter scale'. I'd simply mean that the model is a quarter of the size of the original such that something that was twelve feet tall in real life would be 3 feet tall as a model. Similarly if the real thing was 200mm long, the model would me 50mm long. It really doesn't matter what units of measure you use just so long as the measurement on the model is a quarter of the measurement on the real thing. Simple huh?
I also doubt that anybody will struggle if instead of saying 'quarter scale' I say '1/4 scale' as pretty much everybody is familiar with that way of writing a fraction.
Moving on from that it should now be fairly obvious what it means by 72nd scale or 1/12 scale.
Okay, so we're happy with scales being expressed as fractions but in fact scales are actually ratios: they are a ratio of the actual size to the six of the model. Thus instead of saying 1/4, 1/12 or 1/35 scale we say 1:4, 1:12 and 1:35
It may seem silly to have two ways of writing the same thing however it's is the case that while writing a scale as a ratio is the correct way to do it, writing it as a fraction is more widely understood so we tend to see both, with fractions being used more where the general public are involved and ratios being used by boffins and seasoned model makers.
Another thing that happens in some genres of model making is that the scale is specified as a measurment e.g. 4mm or 28mm scale. In fact there are two different systems in common usage:
The first, which is often used by railway modellers, is to state a single figure Xmm as an an abbreviation of "Xmm to the foot". What they are really saying therefore is that Xmm on their model equates to 1 foot in the real world. 2mm and 4mm are fairly common scales used by railway modellers.
The second system is used with figures and is used as an indication of the height of the figure e.g. 28mm or 54mm. To make things even more complicated however there is some debate as to whether this refers to the height of the figure or the height up to the eyes. The thinking behind the latter is that most of the (military) figures are wearing hats or helmets so you can't see how tall they are. While this sounds sensible, either suggestion assumes that all manufacturers will conform to the same thinking (and clearly they don't) and that every soldier in every army is exactly the same height. Clearly real soldiers are not all at same height so there's no good reason that model soldiers should be all the same height either. When the scale of a figure is described as 28mm or 54mm, work on the basis that it's a rough guide as opposed to an accurate measure.
Another expression of scale is which is in common usage is that used in railway modelling where people use terms like N gauge and HO/OO gauge. This IS correct as it refers to the distance between the rails however you will also here people refer to N and HO/OO as if they are scales. This is not really correct but happens because for each of the gauges there is commonly used scale, often with a 'nasty' number when described as a ratio, and it's easier to refer to the gauge rather than the scale.