Abstract: The present document describes a flow measuring apparatus for measuring a flow of particles through a section of a fluid dispensing apparatus, comprising at least one photo-detection device comprising a light source and a detector, wherein the light source is configured to emit electromagnetic radiation onto the detector along a light path, wherein the detector is configured to measure disturbance of the electromagnetic radiation by the flow of particles to provide measurements of the presence, mass and velocity of particles within said section of a fluid dispensing apparatus. Also described is an inhalation apparatus for drug delivery by inhalation comprising a flow measuring apparatus of the present invention.