The mechanical load on a rolling element bearing is determined from the deformation of the rolling element bearing. The local deformation caused by the rolling contact forces is used to determine an average contribution to the mechanical load in order to average out the effect on the deformation as a result of the spread in diameter of the rolling elements of the bearing. The global deformation of the rolling element bearing is determined to calculate a dynamic contribution to the mechanical load. The dynamic contribution takes into account the variations of the mechanical load on the relevant time-scales that have been omitted from the average contribution as a result of the averaging operation. The total mechanical load is the sum of the average contribution and the dynamic contribution.