Automatic process for calibrating the single and double dose of ground and dispensed coffee by means of a specific grinder-doser integrating a weighing device with a load cell. The process is automatically and steadily carried out during the ordinary activity, with no interruptions, adapting the grinding time according to the actually detected grammages, in order to get closer as much as possible to the desired grammage in any use condition. The process, after a preliminary phase for temporary configuring the desired grammages and the grinding time, conceives self-calibration cycles continuously repeated, each of them comprising three sequential phases: a first phase for automatically checking the dispensing with progressive weight detections, a second phase for automatically processing the detected data for determining the correct grinding time, a following third phase for the automatic setting.