The invention relates to a method for determining and indicating the quantity of a liquid or solid stored material contained in a container sealable with respect to the atmosphere or any other reference gas pressure, together with a residual volume of the gas interior representing the total volume less the stored product volume, the residual volume being increased and/or decreased after sealing the container by means of a displacer with a freely adjustable displacement size and shape arranged within the container and the resulting pressure change in the residual volume is determined as the measured value for the latter by means of the gas pressure measuring device permanently connected to the container gas zone, so that the corresponding apparatus can be produced with reduced costs and space requirements, has no special sealing problems and simultaneously satisfies at least the same requirements as regards accuracy of measurement and indication, response, adjustability and functional reliability as the known apparatuses and also without using additional external containers or precision pump cylinders and pistons ensures that the product stored in the container is reliably and accurately determined.