Summary 1. All materials change size with temperature change, and over small temperature changes the relative size change (DL/L) is proportional to the temperature change, and the proportionality constant is the Coefficient of Thermal Expansion (CTE). 2. The CTE is very dependent on the details of the makeup of the material. Generic terms like "steel" or "ceramic" are virtually useless. 3. Given the exact type of material (e.g. AISI 52100 Steel) the CTE can be looked up in reference books, or sometimes obtained from the manufacturer. The uncertainty of the number is generally not available. 4. Reference books and manufacturers generally have the average CTE over some temperature range. Often the range contains the dimensional reference temperature of 20 °C, but the value at 20 °C is seldom available. Book values generally are the average over at least 80 °C, and often 3 or 4 times as much. Since most metals have CTE that rise with temperature, an average CTE for 20-100 °C is generally biased if used at room temperature. This bias is typically a few percent, but using an average CTE over larger temperature ranges can result in biases of 10% or more. | 
