Thermal expansion can be three types:
Linear expansion
$$\alpha_l = \frac{1}{\Delta T} \frac{\Delta l}{l}$$
Area expansion
$$\alpha_a = \frac{1}{\Delta T} \frac{\Delta A}{A}$$
Volume expansion
$$\alpha_v = \frac{1}{\Delta T} \frac{\Delta V}{V}$$
Thermal expansion can be three types:
$$\alpha_l = \frac{1}{\Delta T} \frac{\Delta l}{l}$$
$$\alpha_a = \frac{1}{\Delta T} \frac{\Delta A}{A}$$
$$\alpha_v = \frac{1}{\Delta T} \frac{\Delta V}{V}$$