The development of a novel and accurate thickness identification methodology is imperative for the continued study and potential commercialization of two-dimensional (213) materials. Through experimentation, an effective and straightforward methodology has been produced for the thickness identification of MoS2 and In2Se3 nanosheets on 300nm Si/SiO2 under optical microscopy from approximately single to decuple layer numbers. The optical contrast difference values of the atomically-thin nanostructures were collected throughout and arranged into a standard reference index which was correlated to height number in nanometers. Using this method, the thickness of a substance could be simply and accurately determined without the use of complex instrumentation, experimental setup, and calculation, therefore, saving time and financial costs.