Moelling 3' gauge railroads is part of the hobby of rail transport modelling. Specifically it relates to the modelling of narrow gauge prototypes of 3 ft (914 mm) gauge. This gauge was the most common narrow gauge in the United States and in Ireland. Apart from some other lines in North, Central and South America, 3 ft (914 mm) gauge was uncommon elsewhere. Therefore most 3 ft (914 mm) gauge modellers model either United States or Irish prototypes.