Why doesn't mass change when measured on the moon instead earth?

Mass is a measurement of the amount of matter.

Explanation:

Mass measures the amount of matter in an object. The amount of matter in an object stays constant whether on Earth or on the moon.

Weight, however, is the measurement of the gravitational attraction on a body (of matter). Earth pulls you towards it with a stronger gravitational force than the moon would, due to its larger mass.

Answer:Mass is a measurement of the amount of matter.