Amount of matter in an object or a measure or the inertia of an object is called?

Answer: mass

Mass is defined as the amount of matter that makes up a body; which is measured by its inertia.

It should be noted that inertia is a property of bodies or objects that is related to resistance to changes in its state of motion. So, the amount of inertia that a body possesses depends on its quantity of matter, that is, its mass.