Strain ($ϵ$) is a measure of the deformation of a body relative to its original dimensions. For longitudinal deformation (tensile or compressive): $\text{Strain}=\frac{\text{Change in Length (}\Delta L\text{)}}{\text{Original Length (}L\text{)}}$

• Units: Since it is a ratio of two identical physical quantities, strain is a dimensionless and unitless quantity. Other types include volume strain ($\Delta V/V$) and shear strain (tangential displacement divided by height).