G scale is a scale for model railways, and the most popular scale for garden railways - indeed this explains the name. Originally and correctly, G scale is the use of 45mm gauge track, as used in standard gauge I scale (NEM 010), aka 3/8" scale (NMRA S-1), for modelling metre gauge narrow gauge railways, using the correct scale of 1:22.5. Metre gauge is the most common narrow gauge in Europe.

In the United States, the commonly used narrow gauge is 3 feet; modelling this correctly with a 45mm track gauge gives a scale of 1:20.3, which is commonly used by American manufacturers. Correctly speaking, these are not really G scale, but they are frequently called that. Some people call 1:20.3 "F scale". Other scales are used to model other narrow gauges; although some call models of standard gauge equipment to 45mm track gauge 'G scale', these models are actually I scale (NEM) or 3/8" scale (NMRA).

The major European manufacturer, and the one that really made garden railways popular, is Ernst Paul Lehman Patentwerk , and is sold under the brand name of LGB (Lehmann Gross Bahn or Lehmann Big Train). The company was founded in 1881 and started producing LGB in 1968. Today it produces models of European and US originals, of steam, diesel and electric prototypes as well as a large range of coaches, trucks and accessories.

LGB track is made of brass and so can remain outside in all weathers - a quick wipe and it is ready for use. Track can also be had in equally durable stainless steel, but it is significantly more expensive.