The coupling load measurement method allows to measure load between a first driving shaft and a second driven shaft connected by a hub coupled both with the first shaft and with the second shaft by at least one flexible coupling element coupled to the hub and to the first shaft and/or to the second shaft; the method comprises, during operation of the shafts, a measurement step of measuring a distance variation respect to a reference distance between a first flange of the hub and a second flange of the flexible coupling element and the step of using the measured distance variation for calculating the load.