Method of determining the average droplet size of ink droplets released by an ink jet printer, the inkjet printer comprising • a control unit, • an ink reservoir, the ink reservoir having a substantially predetermined volume • a print head comprising a plurality of nozzles and ink channels arranged side by side, each nozzle being connected to the ink reservoir via its associated ink channel • a dispensing device for dispensing ink pellets of substantially predetermined and identical volume to the ink reservoir; • a carriage carrying the print head, the carriage being moveable for disposing the print head beneath the dispensing device, • first counting means for counting a number of ink pellets dispensed to the reservoir, • second counting means for counting the number of ink droplets released by the nozzles, • detecting means for detecting the ink level within each ink reservoir; the method comprising the steps of: A) measuring an amount of ink dosed to the ink reservoir by the first counting means by counting the number of ink pellets dispensed to the ink reservoir of the print head of the inkjet printer; B) measuring the ink level within said ink reservoir by the detecting means, C) measuring the number of ink droplets released by at least one nozzle operatively connected to the ink reservoir by the second counting means by counting the number of ink droplets released by the nozzles, and D) determining the average ink droplet size by the control unit based upon the measured values gathered in steps A) - C); and F) controlling the dispensing device and the carriage by the control unit to timely supply the ink reservoir with sufficient ink dependent on the printing tasks to be performed within a certain timeframe and to optimize the print quality of the inkjet printer permanently on the actual average droplet size determined by the control unit. • a control unit, • an ink reservoir, the ink reservoir having a substantially predetermined volume • a print head comprising a plurality of nozzles and ink channels arranged side by side, each nozzle being connected to the ink reservoir via its associated ink channel • a dispensing device for dispensing ink pellets of substantially predetermined and identical volume to the ink reservoir; • a carriage carrying the print head, the carriage being moveable for disposing the print head beneath the dispensing device, • first counting means for counting a number of ink pellets dispensed to the reservoir, • second counting means for counting the number of ink droplets released by the nozzles, • detecting means for detecting the ink level within each ink reservoir; A) measuring an amount of ink dosed to the ink reservoir by the first counting means by counting the number of ink pellets dispensed to the ink reservoir of the print head of the inkjet printer; B) measuring the ink level within said ink reservoir by the detecting means, C) measuring the number of ink droplets released by at least one nozzle operatively connected to the ink reservoir by the second counting means by counting the number of ink droplets released by the nozzles, and D) determining the average ink droplet size by the control unit based upon the measured values gathered in steps A) - C); and F) controlling the dispensing device and the carriage by the control unit to timely supply the ink reservoir with sufficient ink dependent on the printing tasks to be performed within a certain timeframe and to optimize the print quality of the inkjet printer permanently on the actual average droplet size determined by the control unit.