Flexural stiffness is defined as the torque required to bend a solid structure per unit of curvature produced. In a beam, the flexural stiffness varies as a function of the distance to the support point x following the equation:.

where E is the Young's modulus, I is the second moment of inertia, y is the transverse dislocation of the beam at x, and M(x) is the moment at x. Flexural stiffness has SI units of Pascal multiplied by meter raised to the fourth power (or equivalently N "Newton (unit)")·m²).