In rail transport, track gauge is the distance between the inner edges of the rail heads.

For various reasons, the track gauge on different railways in different countries of the world is different. This creates certain difficulties, especially for international freight transport by rail.

To overcome this, the following are used:

• transshipment of goods from rolling stock intended for use on railways of one gauge to wagons of another gauge;
• rearrangement of wagons on wagon bogies designed to move along a certain track;
• various technologies for automatic track gauge change.

For these purposes, at the connecting points, and often for many tens of kilometers in both directions, there can be railway tracks with different gauge widths or combined multi-gauge railway tracks.

Wide track gauge

Russia, Mongolia, Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, Uzbekistan, Azerbaijan, Georgia, Belarus, Moldova, Ukraine, Estonia, Latvia, Lithuania, Finland, northern Afghanistan – 1520 mm

Standard gauge

Turkey and European countries (the most common track size in the world) – 1435 mm.

China, Iran, South Korea – 1435 mm

Maximum track size

India, Pakistan – 1676 mm.