The **moment of inertia** (symbol *I*, SI unit kg·m^{2}) of a rotating object is a measure of what angular acceleration will be produced by a given torque, and can therefore be thought of as the rotational equivalent of mass. It is defined as

For a point mass, it is equal to the distance from the centre of rotation squared times the mass of the object, or

The moment of inertia is also equal to angular momentum divided by angular velocity, or