Typical scales of models

Model aircraft

The premier scale for model aircraft vehicles is 1:72. Airliners are at 1:144, with a few at 1:288. A scale with more room for detail is 1:48. Other, arguably more luxurious, models are available at 1:32 and 1:24. A few First World War aircraft were offered at 1:28 by Aurora. Other scales which failed to catch on are 1:64, 1:96, and 1:128. Repressings of old moulds are often revived in these scales, however. There are also the most common carrier aircraft at the scales of their ships (see below).

Although the Soviets did not supplant 1:48 with their scale 1:50, nor 1:32 with their scale 1:30, the Japanese tried to offer the scale 1:100. There is a major European project to bring about 1:150 to replace 1:144, just as they have small toy airliners in decimalized scales. And the French firm Heller SA, unlike any other in the world, offers models in the scale 1:125.
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Model rockets and spacecraft

Model rocket kits began as a development of model aircraft kits, yet the scale of 1:72[V.close to 4mm.::1foot] never caught on. Scales 1:48 and 1:96 are used. There are some rockets of scales 1:128, 1:144, and 1:200, but Russian firms put their large rockets in 1:288. Heller is maintaining its idiosyncratic standard by offering some models in the scale of 1:125. Fantasy spacecraft, of course, can be of any scale, as they aren't going to be compared to anything on this planet.
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Model railways
An HO scale model railroad
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An HO scale model railroad

Main article: Rail transport modelling

Model railways use the term "gauge", referring to the width of the tracks just as full-size railways do. Although railways were built to many gauges, generally it's the 'standard gauge', 4ft 8.5inch, that is referred to, as it is in this section. Meaning the distance between the inside vertical edge of opposing rails, gauges for model railways were originally in inches, but later they were standardized in metric units, even for companies which put models in traditional Architect's gauge proportions on such metric tracks. A range of scales were accepted by model railroaders for each gauge for mere convenience's sake.

The most popular scale to go with a given gauge was often derived at by the following roundabout process. German artisans would take strips of metal of standard metric size to make things to blueprints whose dimensions were in inches: hence "4 mm to the foot" yields the 1:76.2 size of the "00 gauge". This British scale is anomalously used on the standard H0 gauge (16.5 mm) tracks, however, because early electric motor magnets were awkward in small 3.5mm/foot loco. models.

The Germans have a more developed terminology, which can explain this a bit better. Baugrösse (English: "building size") is the alphanumeric designation, which has nothing to do with physical measuring. It's used for gauge, as in "No. 1 gauge", "HO gauge", or "Z gauge". Maßstab (English: "measure") is the proportion, with a colon, as in the corresponding terms "1:32", "1:87.1", and "1:220". Spurweite (English: "track width") is the distance between the tracks, or correspondingly "1¾-inch", "16.5 mm", and "6.5 mm", and again gauge is used for this in English. One might add to these the old use of the term scale, of "3/8 inch to the foot" and "3.5 mm to the foot" for the first two, while the last really isn't expressible in this manner. Early 1900s German mass-produced toys had a measured gauge from rail centre to rail centre of rolled tinplate rail, with much latitude between flange & rail.

There are three different standards for the "0" Gauge, each of which uses tracks of 32 mm for the standard gauge. The American version continues a dollhouse scale of 1:48. It is sometimes called "quarter-gauge", as in "one-quarter-inch to the foot". The British version continued the pattern of subcontracting to Germans; so, at 7 mm to the foot, it works out to a scale of 1:43.5. Later, MOROP, the European authority of model railroad firms, declared that the "0" gauge (still 32 mm) must use the scale of 1:45. That is, in Europe the below-chassis dimensions have to be slightly towards 4ft. 6 inches, to allow wheel/tyre/splasher clearance for smaller than realistic curved sections.

"Live steam" railways, that you actually ride on, are built in many scales, such as 1-1/2", 1", and 3/4" to the foot. Common gauges are 7-1/2" (Western US) and 7-1/4" (Eastern US & rest of the world), 5", 4-3/4". Smaller Live Steam gauges do exist, but are hardly "rideable".