Weight is a measurement of the force placed on an object by gravity, whereas mass is the amount of matter an object contains. Mass is commonly denoted using m or M, and weight is denoted with W.
Mass is commonly measured in grams and kilograms, whereas weight is generally measured in Newtons. Weight changes depending on location, while mass is always constant. For example, weight on the moon is less than weight on Earth. Weight is contingent on gravity; therefore, objects are heavier when gravity is greater. Gravity does no affect an astronaut's body in space, so the astronaut is essentially weightless. While the amount of mass can never reach zero, weight can equal zero.