A method for dimensioning a filter group for internal combustion engines, provided with a first filter wall and a second filter wall, located downstream of the first filter wall with reference to a direction of a fuel, configured such as to be crossed in series by the fuel, characterised in that it comprises steps of: a) supplying the fuel into the filter group at a minimum fuel flow (Q), destined to guarantee start-up and functioning of the engine in normal operating conditions thereof; b) calculating a pressure drop across the first filter wall; c) calculating a pressure drop across the second filter wall; d) modify morphological and shape characteristics of the first filter wall up until when the pressure drop in the first filter wall exceeds the pressure drop in the second filter wall.