Linear, Area & Volume Expansivity
The linear expansivity (α) of a substance is the fractional increase in its length per degree change in temperature.

α = L2 - L1/L1 ( θ2 - θ1 )

'L' denotes Length

The area expansivity (β) of a substance is the fractional increase in area per degree change in temperature.

β = A2 - A1/A1 ( θ2 - θ1 ) | β = 2α

'A' denotes Area

The volume expansivity (γ) of a substance is the fractional increase in volume per degree change in temperature.

γ = V2 - V1/V1 ( θ2 - θ1 ) | γ = 3α

'V' denotes Volume

Note: Δθ = θ2 - θ1

As the case may be, 'e' = L2 - L1 | e = Extension

As the case may be, 'e' = A2 - A1 | e = Extension

As the case may be, 'e' = V2 - V1 | e = Extension