A system for filling pre-charged aerosol cans comprising a frame, a power actuator on the frame having an output member that extends forcibly downwardly through a stroke of fixed length and retracts upwardly, a combined reservoir and filling head supported in the frame generally below the output member, the filling head having a cylindrical dispensing bore and an outlet below the bore adapted to be coupled to the valve of the aerosol can, a dispensing piston with a lower face operable in the bore to create hydraulic pressure on liquid received in the bore from the reservoir, a set of cooperating elements for coupling a dispensing piston to the output member selectively at a plurality of predetermined fixed spacings from the output member, whereby the volume of fluid displaced from the dispensing chamber by the dispensing piston is regulated to fill cans of different capacity while the output member of the power actuator traverses its stroke of constant length.