Method and apparatus are disclosed for measuring an apparent viscosity of a non-Newtonian fluid. The method and apparatus involves calculating a power-law number n relating a shear stress of the fluid to a shear rate of the fluid, and then calculating an estimated apparent viscosity ηest of the fluid at a selected shear rate based on a yield stress Y of the fluid and on the calculated power-law number n. The estimated apparent viscosity of the fluid at a selected shear rate is calculated based on the experimental observation that reference shear stress is 1.5 times the yield stress for most shear thinning fluids (e.g., grease).