**The SI units for moment of inertia are kg m^2.** For a point mass, the moment of inertia equals mass times radius squared, so other mass units (such as pounds) and other distance units (such as feet) are occasionally used instead.

A specific axis of rotation must be defined to calculate the moment of inertia since it measures an object's resistance to a change in rotational direction. Multiple point masses or continuous objects have a moment of inertia that is the sum of all the point masses within the object. For continuous objects this is found by integration. There are known formulas to calculate the moment of inertia for common shapes like cylinders or rods.