A device for monitoring the mass of a fluid remaining in a tank as the fluid periodically or continuously leaves the tank includes a housing comprising an inlet adapted to be attached to an outlet of the tank and to receive fluid from the tank. A flow meter measures a plurality of flow rate measurements of the fluid as it leaves the tank. At least one processor is configured to determine a mass of the fluid that has left the tank during at least one measurement period, determine a mass of the fluid remaining in the tank based at least partially on an initial mass of the fluid in the tank and the determined mass of the fluid that has left the tank, and generate, based on the mass of the fluid remaining, an indication.