We report a technique to determine the coverage of metallic thin films by analyzing layer-resolved surface states with photoemission by using atomically flat Ag/ Au͑111͒ thin films as a test system. We analyzed the surface state on Au͑111͒ covered with Ag up to 4 ML with atomic resolution, and precisely determined the total Ag coverage of Ag/ Au͑111͒ through a line-shape analysis. With precise measurements of the absolute coverage of thin films becoming possible, one can calibrate the tooling factor of evaporators with unprecedented accuracy.