G scale model trains are 1:22, that is 1/22 the size of a real train. Because of their size these trains are usually found outdoors, and are big enough to carry a passenger. G trains vary in actual size, depending on which prototype train [real sized train] they are modeled on, but they all run on Gauge 1 track.
Originally designed and sold by the German company, Lehmann Patentwerk in the 1960s, they were sold under the brand of LGB [Lehmann Gross Bahn or in English, "Lehmann Big Train"]
It is the ‘G’ from ‘gross’ that gives this scale its name – G scale
Because so many of these larger trains have been set up on outdoor layouts, they became known as ‘Garden Trains’ and many people incorrectly believed that the term G Scale meant Garden Scale