Hooke's Law:

According to this law, within the elastic limit, the stress is directly proportional to the corresponding strain. That is,

Stress ∝ Strain

or, Stress/Strain = Constant (E)

The constant of proportionality, E, is a measure of elasticity of the material and is called modulus of elasticity. As strain is a dimensionless quantity, modulus of elasticity has the same dimensions (or units) as that of stress. Its value is independent of stress and strain; it depends on the nature of the material.