In physics, the parallel axes rule can be used to determine the moment of inertia of a rigid object about any axis, given the moment of inertia of the object about the parallel axis through the object's center of mass and the perpendicular distance between the axes.

Let I_G denote the moment of inertia of the object about the center of mass, M the object's mass and a the perpendicular distance between the two axes. Then the moment of inertia about the new axis is given by:

This rule can be applied with the stretch rule and perpendicular axes rule to find moments of inertia for a variety of shapes.