Simplifying and rearranging gives, This equation gives the bending normal stress, and is also commonly called the flexure formula. The y term is the distance from the neutral axis (up is positive). The I term is the moment of inertia about the neutral axis.

Keeping this in view, how is bending moment calculated?

It is calculated as the perpendicular force multiplied by the distance from the point. A Bending Moment is simply the bend that occurs in a beam due to a moment. It is important to remember two things when calculating bending moments; (1) the standard units are Nm and (2) clockwise bending is taken as negative.