Where possible, we list the capacity of our ink cartridges in ml. However, this in itself is not particularly useful, so we also include an estimated page yield along with a cost-per-page (which is simply the price of the cartridge divided by the number of pages expected).
The page yield is a better number to use for comparing cartridges (and overall running costs of printers) because different printer technologies use ink at different rates. A 12ml cartridge in an Epson printer may not produce the same number of pages as a 12ml cartridge in a Canon printer. Sometimes, different printer ranges from the same manufacturer will give different results for the same quantity of ink.
To provide a fair comparison between different printers and cartridges, an international standard (ISO/IEC 24711 and 24712) was introduced. This defines a series of five "typical" documents which are used in testing to establish the number of copies that a cartridge will print. The test documents look like this:
FACTORS AFFECTING PAGE YIELD
The tests run by manufacturers are obviously done in ideal conditions in order to maximise the number of pages that they can quote for their cartridges. The biggest difference between the test conditions and an average user's conditions is that the test documents are printed continuously until the cartridges go from full to empty. Therefore they do not take into account the tiny amount of ink (1-3 pages worth) that most printers use to prepare the nozzles when the printer is turned on. If your average use consists of turning your printer on, printing one page and turning it off again, your estimated page yield can be reduced by up to three quarters!
Runnning a cleaning process also uses ink, usually around 2-5% depending on the printer and cartridge.
If you're printing text, then the font style and size can make a big difference. Large sizes (eg headings), heavy print (bold) and underlining will significantly reduce your page count. A simple sans-serif font such at Calibri or Tahoma will give you more pages than the same text in a serif, complex or bold font such as Times New Roman or Arial Black.
When printing spreadsheets, think twice before using cell borders - you'll get about half as many pages if you do.
PAGE YIELD FOR PHOTOGRAPHS
There is no established standard for ink usage when printing photographs. This is simply because of the huge variation that can come from the size, subject, paper type and print quality selected.
As a general rule, the standards for general page yields are based on a page coverage of approximately 5%, while photographs can be anything between 50% and 90%.
Printing A4 photographs will result in a page yield of less than one tenth of the rated numbers.