Development of a gas turbine engine starts with optimization of the working process parameters. Turbine inlet temperature is among the most influential parameters that largely determine performance of an engine. As typical turbine inlet temperatures substantially exceed the point where metal turbine blades maintain reasonable thermal strength, proper modeling of the turbine cooling system becomes crucial for optimization of the engine’s parameters. Currently available numerical models are based on empirical data and thus must be updated regularly. This paper reviews the published information on turbine cooling requirements, and provides an approximation curve that generalizes data on all types of blade/vane cooling and is suitable for computer-based optimization.