The falling cylinder viscometer (FCV) has been investigated both theoretically and experimentally. Although the use of this instrument goes back to the early work of Bridgeman because of its suitability for high pressure measurements, a fundamental study of the flow field around the cylinder has not yet been reported. The study presented here allows the prediction of end effects without resorting to empirical corrections or instrument calibration. The investigation was carried out over a wide range of cylinder diameters and lengths and an operating parameter, the Geometry Number, has been defined which characterizes the FCV and is solely determined by the dimensionless cylinder diameter and length. A correlation equation from which the Geometry Number can be calculated is presented which can be used to design viscometers for particular applications. The agreement between the analytical and experimental results of the Geometry Number, the measured viscosity of standard fluids and the repeatability and accuracy are all within one percent. Both the theoretical analysis and experimental data indicate that falling cylinder viscometers based on the correlated equation can be accurate and absolute viscometers.