To start off you need to know that the mass of an object never changes. But gravity does. Think about it life this. Gravity is less on the moon but more on earth, therefore, gravity can change, but mass can't. Now its almost the same as weight because weight changed based upon the gravity. On the moon you weigh only about 10 pounds, on earth, you way much more, and so on.
To calculate the formula you have to do Mass×Gravity which can calculate into Weight.
~Evie
