The measure of inertia is mass/05%3A_Newtons_Laws/5.03%3A_Mass_and_inertia). Mass is a measure of how much matter is in an object, and the more mass an object has, the more inertia it has. Inertia is the property of an object to resist changes in its motion, and it is directly proportional to the mass of the object. The greater the mass of an object, the greater its inertia, and the harder it is to change its state of motion/05%3A_Newtons_Laws/5.03%3A_Mass_and_inertia). Therefore, mass is the measure of inertia of an object.