The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of thickness. For example, syrup has a higher viscosity than water.

A viscosity meter (also called viscosimeter) is an instrument used to measure the viscosity of a fluid. Rotational viscometers with rotating spindles or rotors are the most common tools used to measure the shear viscosity of fluids. A viscometer is frequently used in laboratories, but it also has practical applications in factories and other industrial environments. Viscometers can be used in laboratory, food & dairy industries, pharmaceuticals, lubricants, adhesives, paints & inks, cosmetics, etc. with countless applications.