ISO standards – and impartial measurements
Spencer Labs specializes in testing printer page yields, and providing the information necessary to calculate cost per page - that is the unit cost of printing: Laser vs. Inkjet, and different models within the types of printers. As an independent lab, a number of different printer manufacturers use them to estimate cost per page. Spencer labs say, “a relevant, standard test Document is required. Since the yield may vary print-to-print on many printing systems, meaningful estimation of how many prints can be printed from an ink or toner cartridge requires actual testing of representative sample cartridges"
For black text, a document is created in a given text size, with specific margins. A new cartridge is put in the printer, and the document is printed until the ink runs out, or the cartridge is evaluated as empty by the printer software. The resulting copies are counted.
For color, a document is created with text and business graphics, such as a pie chart. Although I don’t remember reading this, I assume that the graphics will use roughly the same amount of each color. The document is printed until a cartridge is emptied. With most printers using tri-color cartridges, if one color is depleted, the printer usually will not allow additional prints. Again, the pages printed are counted. Black cartridges are often rated for a higher number of pages than colored cartridges, so the colors are the first to run out. With somewhat higher end printers, instead of a tri-color cartridge, there will be individual color cartridges. However, most printers require that the emptied color be replaced before additional copies are printed
Testing labs repeat this to average the yield of inkjet cartridges or toner cartridges.