This document specifies a method for the measurement of effective focal spot dimensions above 0,1 mm of X-ray systems up to and including 1000 kV tube voltage by means of the pinhole camera method with digital evaluation. The tube voltage applied for this measurement is restricted to 200 kV for visual film evaluation. The imaging quality and the resolution of X-ray images depend highly on the characteristics of the effective focal spot, in particular the size and the two dimensional intensity distribution as seen from the detector plane. This test method provides instructions for determining the effective size (dimensions) of standard (macro focal spots) and mini focal spots of industrial X-ray tubes. This determination is based on the measurement of an image of a focal spot that has been radiographically recorded with a pinhole technique and evaluated with a digital method. For the characterization of commercial X-ray tube types (i.e. for advertising or trade) it is advised that the specific FS values of Annex A are used.