The track gauge expresses the distance between the inner edges of the rails, measured according to convention 14 mm below the top of the rail. It is given in millimeters, although historically used values of nominal gauges arose mostly from measurements in English units. The track has a nominal gauge in the straight section of the track and in curves of larger radii. In curves of smaller radii (on normal gauge lines, this refers to curves with a radius of 300 m and smaller), the gauge is usually widened to make it easier for railway vehicles to pass through them. The expansion varies from a few millimeters to a few centimeters – depending on the gauge of the track and the radius of the arc. The actual gauge value is measured by gauge. In places where it is necessary to run rails of several gauges along one track, if there is a lack of space, a rail splice can be used.
The so-called Stephenson gauge is referred to as the normal gauge, which was enacted as a uniform gauge in Britain in 1846 in a nominal value corresponding to 1435 mm and is today the world’s most widespread gauge. The same track gauge does not automatically mean that all vehicles are transferable between two systems. A significant obstacle can also be the difference in the geometry of the rails and the wheels (e.g. the impossibility of driving a railway wheel on a tramway rail), the passage cross-section or other parameters.
- 3000 mm: unrealized Breitspurbahn (from the time of Nazi Germany),
- 2134 mm (7 ft): until 1892 the gauge of England’s Great Western,
- 2000 mm: Cairngorm Mountain Railway, Scotland (length 2 km, in operation 2001-2018),
- 1829 mm: the first railway line in Tsarist Russia
- 1828 mm (6 ft): Erie Railroad to 1880
- 1800 mm: Oberweißbacher Bergbahn;
- 1,676 mm (5 ft 6 in): Argentina and India broad gauge, Pakistan, Bangladesh, San Francisco BART; in the literature it is often mistaken for Spain;
- 1674 mm (5 Castilian feet): Spanish broad gauge (also 1672 mm);
- 1668 mm: Iberian broad gauge currently used uniformly in Portugal and Spain;
- 1664 mm: Portuguese broad gauge,
- 1,600 mm (5 ft 3 in): wide gauge in Ireland, south-east Brazil and Australia,
- 1587 mm: tram in New Orleans (USA),
- 1581 mm: Pennsylvania streetcar gauge in Philadelphia and Pittsburgh (USA);
- 1,524 mm (5 ft): old Russian broad-gauge nominal, currently only used by Finland;
- 1520 mm: Russian broad gauge, current nominal value since the second half of the 20th century, when the dimension was adjusted to approximate the metric system; also used in other states of the former Soviet Union, in Mongolia and Afghanistan.
- 1219 mm (4 feet): Glasgow Underground Railway – Scotland,
- 1200 mm: Switzerland – Rheineck–Walzenhausen Railway at Lake Constance, 1106 mm (3.5 Austrian feet): České Budějovice – Linz – Gmunden Coal Railway and Hausruck Coal Railways,
- 1100 mm: Germany – tram in Braunschweig and in Brazil – Rio de Janeiro, ex Lübeck and Kiel,
- 1067 mm Cape gauge (3.5 ft): widespread in southern Africa, Japan, Australia and New Zealand, Tallinn tram service
- 1050 mm: Hijaz Railway in Syria, Jordan and originally also in Saudi Arabia,
- 1009 mm: tram in Sofia,
- 1000 mm meter gauge: the basic gauge of railways, for example, in Kenya and other Central African countries, an extensive railway network in India and Brazil; very wide gauge of narrow-gauge railways and trams in Germany (including already abolished networks of Sudeten cities in the Czech Republic), Switzerland, Spain and Portugal, tram line Liberec–Jablonec, tram in Bratislava, Tatranské elektrische železnice, ground cableway Starý Smokovec – Hrebienok
- 991 mm (3 ft 3 in): Commonwealth countries,
- 950 mm: Italy – Italian “standard” narrow gauge, also Eritrea – former Italian colony,
- 925 mm: formerly trams in Saská Kamenice,
- 915 mm: Peru,
- 914 mm (3 ft): New Zealand, Isle of Man, Cuba, Denver & Rio Grande Western in the US,
- 900 mm: Mining railway in Sokolov (discontinued 2004), German Molli narrow gauge between Bad Doberan and Kühlungsborn, in the world of trams and industrial railways,
- 891 mm (3 Swedish feet): Sweden,
- 880 mm: Sundland Torvströfabrikk industrial track in Norway
- 838 mm (2 ft 9 in): Commonwealth countries,
- 800 mm: roller coasters in Switzerland – for example Wengernalpbahn,
- 791 mm: narrow gauge in Denmark,
- 785 mm: narrow-gauge railways in Poland and Eastern Europe,
- 762 mm (2 1/2 ft): narrow-gauge in India, Cuba and Australia; converted to Cape gauge in South Africa,
- 760 mm – Bosnian gauge: narrow-gauge railways in Bosnia, India, Cuba and the countries of the former Austria-Hungary, in the Czech Republic and Slovakia, e.g. JHMD, passenger cars, TREŽ, ČHŽ,
- 750 mm: very widespread gauge in Germany (e.g. Fichtelbergbahn) and countries of the former Soviet Union; military and industrial railways in Argentina,
- 700 mm: military and industrial tracks worldwide,
- 693 mm: Sweden – Industrial railway at Kvarnsvedens Pappersbruk,
- 686 mm (2 ft 3 in): England,
- 650 mm: Morocco.
