There could be several axes possible along which a rigid body can rotate, and hence correspondingly, there could be various moments of inertia for the same body. If the moment of inertia, ICM , about an axis passing through the center of mass is known, then the moment of inertia about any other parallel axis can be obtained using the parallel-axis theorem. The theorem states that the moment of inertia along any axis parallel to the axis passing through the center of mass is given as the sum of ICM and the product of the mass of the body and the square of the perpendicular distance between the two axes. Consider a door of mass M and height 2L. The width of the door is half of the height of the door. The door rotates about its hinges. The ICM of the door is equal to ML2 by twelve. The moment of inertia along the rotational axis is thus given as the sum of ICM and ML2 by four.