Measuring the thickness of a print media supported by a platen or belt by: moving a measurement bar to a first position to contact a surface of the platen or belt, moving the measurement bar to a second position to contact a surface of the print media when supported by the platen or belt, and determining the spatial difference between the first and second positions such as to measure the thickness of the print media. The measurement bar is arranged to cover a width of the print media when supported by the platen or belt.