A method and a system for determining a mass of feedstock discharged by a conveyor during a first time interval Δt are disclosed. The method includes taking successive digital images of the feedstock in a specific zone of the conveyor being separated by a second time interval δt of smaller duration than the first time interval Δt, for each of the second time intervals δt: computing the advancing distance of a sub-volume of feedstock during the second time interval δt in the specific zone of the conveyor by numerical treatment of the two successive images associated with the second time interval δt; determining at least one transversal height profile of the sub-volume of feedstock; and determining an effective feedstock density for the sub-volume of feedstock. The method further includes computing the mass of feedstock discharged by the conveyor during the first time interval Δt into the metallurgical furnace on the basis of the advancing distance, the at least one transversal height profile and the effective feedstock density, computed or determined for each of the second time intervals δt.