A system includes a fluid reservoir, a differential pressure sensor, and a controller. The fluid reservoir has a bottom and is to hold a fluid. The differential pressure sensor is coupled to the bottom of the fluid reservoir and to sense a pressure difference between pressure exerted on the differential pressure sensor by the fluid and pressure exerted on the fluid in the fluid reservoir and to provide at least one signal that indicates a fluid level in the fluid reservoir. The controller is to receive the at least one signal and determine a fluid volume in the fluid reservoir based on the at least one signal. Also, the controller is to provide at least one of a fluid level signal that indicates the fluid level in the fluid reservoir and a fluid volume signal that indicates the fluid volume in the fluid reservoir.