This European Standard is applicable by authorities involved in railway operation and may also be applied for light vehicles (e. g. trams, metros, etc. running on two rails) and their associated infrastructure, but not for systems such as rail-guided buses. It allows vehicles and infrastructures to be dimensioned and their compliance to be checked relative to the gauging rules. For the rolling stock and for the infrastructure, this standard is applicable to new designs, to modifications and to the checking of vehicles and infrastructures already in use. Part 1 of this document covers: the general principles; the various elements and phenomena affecting the determination of gauges; the various calculation methods applicable to the elements shared by the infrastructure and by the rolling stock; the sharing rules for elements taken into account in calculations specific to the infrastructure and to the vehicle; a catalogue of European gauges. This document does not cover: conditions to be met to ensure safety of passengers on platforms and of persons walking along the tracks; conditions to be met by the fixed equipment maintenance machines in active position; the space to be cleared for the running track of rubber-tyred metros and other vehicles; rules applicable to extraordinary transportation, however some formulae may be used; rules applicable to the design of the overhead line; rules applicable to the design of the current collection on a third rail; simulation methods for the running of vehicles, therefore, it does not confirm the validity of existing simulations; verification rules of wagon loadings; coding methods for combined transportation; infrastructure gauges for very small curve radii (e. g. R < 150 m for gauge G1).