The approximate total length of the Channel Tunnel used by Eurostar trains is 50.5 kilometres.
The Channel Tunnel is a railway tunnel beneath the English Channel linking Folkestone in southeastern England with Coquelles near Calais in northern France. Its measured length is about 50.46 km, which is conventionally rounded to 50.5 km.
Construction began in 1988, and the tunnel officially opened in 1994. It consists of two rail tunnels and a smaller service tunnel between them. The rail tunnels carry Eurostar passenger trains, freight trains, and vehicle-shuttle services operated by LeShuttle.
The full tunnel length is not the same as its underwater length. Approximately 37.9 km lies beneath the sea, making it the world’s longest underwater tunnel section. Eurostar trains connect to Britain’s High Speed 1 and France’s LGV Nord, but the Channel Tunnel itself is the cross-Channel link rather than the entire London-to-Paris railway journey.