Provided is a method for determining a performance of a particulate filter of an engine. The method determines an exhaust gas temperature upstream of the particulate filter, an exhaust gas temperature downstream of the particulate filter, and an exhaust gas mass flow upstream of said particulate filter The method further determines a modelled temperature based on the exhaust gas temperature and the exhaust gas mass flow upstream of the particulate filter. A residual value is determined on the basis of the exhaust gas temperature downstream of the particulate filter and the modelled temperature. An equivalent hole size of the particulate filter is then determined using a predetermined function that defines a relationship between the residual value and an equivalent hole size, where equivalent hole size indicates said performance of said particulate filter.