A method and system is disclosed for automatic detection of implement working width of an implement on a vehicle. The method includes tracking location of the vehicle； determining if the vehicle is making substantially parallel passes； if the vehicle is making substantially parallel passes the method also includes determining distances between consecutive passes； and calculating a calculated implement working width based on the distances between consecutive passes. A location sensor attached to the vehicle can be used for tracking the vehicle. Determining if the vehicle is making parallel passes can include grouping the location sensor readings into pass lines that each include sensor readings defining a single pass line； and determining if a current pass line is parallel to a prior pass line. Vehicle heading can be used for determining if pass lines are substantially parallel. Known implement working widths can be used to verify calculated implement working widths.
