Key:gauge
 gauge
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Used to describe the 'gauge' (distance between the inside of the rails) on railways. 
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| Group: Railways |
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| Status: de facto |
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This tag can be used to specify the track width (gauge) of railways. It is specified in millimetres (mm, 1/1,000 of a metre) as is the railway and tagging practice, e.g. gauge=1435 for "1435 mm".
As the Standard gauge of 1,435 millimetres (4 ft 8 1⁄2 in) is used on most of the world's railways, it is particulary important to add the track width for narrow gauge and broad gauge railways, and it is suggested that mappers concentrate on adding this tag to these railways. However, it is not incorrect to add gauge=1435 to a standard gauge railway.
Syntax
The syntax in regular-expression form is \d+(;\d+)*. That is, only numbers, no units (always millimeters), and use semicolons to separate multiple gauges. Anything not in this form (as can be found in taginfo) should be changed.
Why not to use text values
- Main article: Verifiability
Some users used gauge=broad, gauge=standard or gauge=narrow tags. These should be updated with precise information, as there are more than one type of broad/narrow gauges.
Dual gauge tracks
Tracks that support two or more gauges (by using three or more rails) should have all gauges specified using semicolon (";"), no space, as a separator. The smallest value should come first. Example: gauge=1000;1435.