In a system for measuring a fire suppressant or fire suppression propellant quantity, the system comprising: a base (102); a top plate (106) positioned to support a tank (22) of said fire suppressant or fire suppression propellant; a plurality of springs (112) positioned between the top plate and the base to support the top plate atop the base, the plurality of springs positioned to support the top plate along a range of motion between an extended condition and a retracted condition; a first magnetic member (142) mounted to the base; a second magnetic member (140) mounted to the top plate so that a spacing between the first magnetic member and the second magnetic member decreases as the top plate moves from the extended condition to the retracted condition. At least one of the first magnetic member and the second magnetic member is a permanent magnet. A magnetic field sensor (160) is positioned to detect changes in a magnetic field associated with changes in said spacing.