ISO 15312:2018 defines the thermal speed rating for oil bath lubricated rolling bearings and defines calculation principles for the determination of this parameter. The parameter determined in accordance with this document applies to rolling bearings of the given series and sizes of standard design or of a design that, from a frictional point of view, can be related to a standard design bearing.In most cases of standard assembly, the permissible temperature determines the maximum operating speed. Heating of the assembly is then generated by the bearing.Thrust ball bearings are excluded from this document as kinematic effects do not allow the thermal speed rating defined in this document to be applied.NOTE 1 In Annex A mean values for the coefficients f0r and f1r are given ? f0r for calculating viscous losses of oil bath lubricated bearings and f1r for calculating frictional losses of bearings.NOTE 2 Explanatory notes on the limiting criterion are given in Annex B.NOTE 3 In Annex C the reference conditions for grease lubrication are defined. The reference conditions are chosen such that the thermal speed rating for grease lubrication is identical to that for oil bath lubrication.