Materials generally get larger as the temperature increases (however, there are some materials that get smaller with increases in temperature). The amount of this change is characterized by the coefficient of thermal expansion, α, which has the units of 1/(deg Kelvin). The larger the coefficient of thermal expansion, the greater the length change will be for a particular change in temperature. In order to calculate the length change in a particular direction, we need to define the reference temperature, T0, the current temperature, T, and the material length in the direction where the thermal expansion is to be calculated, L. The reference temperature T0 is the temperature at which we consider the material at its initial size and it will get larger for temperatures above the reference temperature and smaller for temperatures below the reference temperature (assuming a positive coefficient of thermal expansion). These variables are defined below:
