Linear expansion is a type of thermal expansion that refers to the change in one dimension (length) of an object due to a change in temperature, usually not including phase transitions. The coefficient of linear thermal expansion (CLTE) is the fractional change in length per degree of temperature change. It is related to the materials coefficient of thermal expansion, which describes how the size of an object changes with a change in temperature. The CLTE is used to estimate the change in length measurements of an object due to thermal expansion.

Linear expansion is a reversible and irreversible swelling caused by the release of residual compressive stresses imparted to the material. It is a common phenomenon observed in solids and liquids. When a solid is heated, it expands and gets bigger, while cooling causes it to contract and get smaller. Similarly, when a liquid is heated, its volume increases, and cooling causes its volume to decrease.

Linear expansion is quantified by the coefficient of linear thermal expansion, which varies with temperature and depends on the particular application and which dimensions are considered important. The coefficient of volumetric thermal expansion is related to the coefficient of linear thermal expansion for isotropic materials.