It is expressed in force per unit area, usually pounds per square inch or kilograms-force per square centimeter. The strain may be a change in length. Young's modulus; a twist or shear, modulus of rigidity or modulus of torsion; or a change in volume, bulk modulus. In the SI, all types of moduli of elasticity are reported in pascals, the conversion factor being one psi = 6.894 757 E+3 pascals. Also known as ELASTIC MODULUS and YOUNG'S MODULUS.