For unsteady state conduction problems in solids, the Fourier number is frequently used as a nondimensional time parameter. Together with the Biot number, the Fourier number can be used to determine the heating or cooling of an object. If the Biot number is less than 0.1, then the entire system can be treated as uniform in temperature. The following equation, derived with the product of the Biot and Fourier numbers, can be used to estimate the time for the object to reach a specific temperature,