The quantitative measure of inertia in an object is its mass. Inertia is the property of an object to resist changes in its state of motion, whether at rest or in motion. According to Newton’s second law of motion, the force required to accelerate or decelerate an object is directly proportional to its mass. Mathematically, force (F) equals mass (m) multiplied by acceleration (a). Therefore, mass serves as a quantitative measure of inertia, with a higher mass indicating greater resistance to changes in motion. This relationship is fundamental in understanding an object’s response to applied forces.