What track gauge does the New York City Subway use?

The New York City Subway uses the standard track gauge of 4 feet 8½ inches.

Track gauge is the distance between the inner faces of the two running rails. New York’s subway inherited this standard gauge from the railways and rapid-transit systems that preceded the unified city network.

The measurement is also written as 1,435 millimeters. It is used throughout the subway despite the system’s historical division among the IRT, BMT, and IND. The separate divisions differ in car dimensions and clearances, but their rails share the same gauge.

People sometimes confuse gauge with car width. Gauge describes the rails, while New York subway cars vary by division: IND and BMT cars are wider than IRT cars. Standard gauge also does not mean that every subway system worldwide uses it; several major systems use different measurements.