Abstract: Fluid level in a container is determined using a single pressure transducer connected to a portable body. The body contains a computer having a memory in which fluid level-to-fluid volume conversion data are stored for different shapes of containers so that fluid volume can be readily obtained for the shape of the respective container once fluid level is determined. These features allow a single monitoring apparatus to be used for monitoring different types of containers. The apparatus preferably includes a radio so that multiple apparatus can communicate in a system with a central remote operator interface device. Fluid level is determined by dividing a pressure reading from the bottom of the fluid by a fluid density determined from two prior pressure reading taken across a known distance (density equals the difference between the two readings divided by the distance).