Abstract: A piezoelectric device is used to determine the viscosity of a fluid. A piezoelectric driver is resiliently attached to a base that is isolated from vibrations. A piezoelectric receiver and a probe are resiliently attached to the piezoelectric driver so that the receiver and probe move in response to motion of the piezoelectric driver, and the piezoelectric receiver gives an electric signal out proportional to motion of the system. The entire system is set to operate near the resonant frequency for the receiver/probe. By applying an oscillating sine wave voltage such as 140 hertz, to the piezoelectric driver, and immersing the probe first in a fluid of known high viscosity, and then in a fluid of known low viscosity, calibrated outputs are obtained from the piezoelectric receiver. Next by exchanging a fluid of unknown viscosity for the known fluids, a third output is obtained that represents the unknown viscosity.