A ridable miniature railway (US: riding railroad or grand scale railroad) is a large scale, usually ground-level railway that hauls passengers using locomotives that are often models of full-sized railway locomotives (powered by diesel or petrol engines, live steam or electric motors).

Typically miniature railways have a rail track gauge between 5 in (127 mm) and under 15 in (381 mm), though both larger and smaller gauges are used.

At gauges of 5 in (127 mm) and less, the track is commonly raised above ground level. Flat cars are arranged with foot boards so that driver and passengers sit astride the track. The track is often multi-gauged, to accommodate 5 in (127 mm), 3+1⁄2 in (89 mm), and sometimes 2+1⁄2 in (64 mm) gauge locomotives.

The smaller gauges of miniature railway track can also be portable and is generally 3+1⁄2 in (89 mm)/5 in (127 mm) gauge on raised track or as 7+1⁄4 in (184 mm)/10+1⁄4 in (260 mm) on ground level. Typically portable track is used to carry passengers at temporary events such as fêtes and summer fairs.^[1]

Typically miniature lines are operated by not for profit organisations - often model engineering societies - though some are entirely in private grounds and others operate commercially.

There are many national organisations representing and providing guidance on miniature railway operations including the Australian Association of Live Steamers and Southern Federation of Model Engineering Societies.

A 'model railway' is one where the gauge is too small for people to ride on the trains. Due to the use of mixed gauge tracks, passengers may ride on a miniature railway which shares the same gauge as, and is pulled by, a large model locomotive on a smaller model gauge, although this is rare.

'Miniature railways' are railways that can be ridden by people and are used for pleasure/as a pastime for their constructors and passengers. In the US, miniature railways are also known as 'riding railroads' or 'grand scale railroads'. The track gauges recognised as being miniature railways vary by country, but in the UK the maximum gauge is 350 mm (13+25⁄32 in).^[2]

A 'minimum-gauge railway', which generally starts at 15 in (381 mm) gauge, is one that was originally conceived as a commercial railway with small gauge track, with a working function as an estate railway, an industrial railway, or a provider of public transport links, such as the Romney, Hythe and Dymchurch Railway, Fairbourne Railway or the Ravenglass and Eskdale Railway.

In the UK, a gauge of 350 mm (13+25⁄32 in) [or above] or crossing a carriageway are the criteria used by the Office of Rail and Road (ORR), at which a railway is no longer classed as miniature and is therefore subject to formal regulation: they may be minor railways and/or heritage railways; the concept of minimum gauge is not recognised for the purposes of regulation.