Scales used for Garden Railways

Gauge '0' - (Scale 1:43.5 in England, scale 1:45 in Europe and scale 1:48 in USA)
Running on 32mm gauge track. Models are of standard gauge railways.

Gauge 'I' - (Scale 1:30.5 in England, Scale 1:32 in Europe and scale 1:32 in USA)
Running on 45mm gauge track. Models are of standard gauge railways.

1/2" - (Scale 1:24 in USA)
running on 45mm gauge track. Models are of narrow gauge railways.

Gauge 'IIm' (1:22.5 in Europe and 1:29 in USA)
Running on 45mm gauge track. Models are of narrow gauge railways. Some models described simply as 'G' scale are actually built to 1:20.3 to represent 3 foot gauge equipment,

5/8" - (Scale 1:19.2 in USA)
Running on 45mm gauge track. Models are of narrow gauge railways.

SM32 & SM45 (1:19 in England)
SM32 running on 32mm gauge track and SM45 running on 45mm gauge track. Models are of narrow gauge railways.

7/8N2 - (Scale 1:13.7 in USA)
Running on 45mm gauge track. Models are of narrow gauge railways and represent 2 foot gauge.

'0' gauge as this is really the smallest that is normally used for live steam. Although working
steam models are built for scales/gauges smaller than '0', these are not common.
'G' scale is commonly used for scale 'IIm' or 'I' running on 45 mm tracks.

Although certain scales are marked as either USA, England or Europe, this is not a strict split of usage and in practice, all versions are found all over the world. They are marked to indicate where they are more commonly used.

NATIONAL MODEL RAILROAD ASSOCIATION
The National Model Railroad Association is the largest organization devoted to the development, promotion, and enjoyment of the hobby of model railroading. The NMRA was founded in 1935 in Milwaukee, Wisconsin in order to provide a service to the hobby of model railroading!