Primarily used as an outdoor garden railway scale, G scale with a 45mm track gauge is used to create narrow gauge railways.
Pioneered by Ernst Paul Lehmann Patentwerk under the brand name LGB (Lehmann Gross Bahn), the first LGB models emerged in 1968 using a track gauge of 45mm. The track scale soon attracted the attention of garden railway enthusiasts because of the robust and more reliable track, coupled with products now available (or previously available) from more than 30 manufacturers around the world. G scale is seldom used indoors because of its size and the space required for track radii.
Though the term 'G scale' is used by many to refer to all models which run on 45mm track – the same gauge as Gauge 1 – G scale refers more to LGB models, with a scale of either 1:22.5 or 1:24. Other terms are adopted for different scales used on 45mm track, such as Gauge 1 in the UK if modelling standard gauge.
If used with 1:22 scale trains, models of metre gauge railways can be created, popular in continental Europe. Any number of narrow gauge or standard gauge models have been produced by manufacturers and enthusiasts to run on 45mm gauge track. Three foot gauge-outline models with a scale of 1:20.3, or 15mm:1ft scale are known in the UK as 'Fifteen Mil', and internationally as FN3 – 'F' for scale, 'N' for narrow gauge and '3' for the gauge.