# Weight vs Mass

Weight and mass are often mistaken for each other, as we use them interchangeably in everyday conversation, but they are two different things.

An object's mass is the amount of matter in it. It is always the same for an object, no matter where in the Universe that object is. It is measured in kilograms (kg) in the SI.

An object's weight is the gravitational pull it experiences in a gravitational field. It depends on the object's position in the field, so it may change from one place to another. Since it is a force, it is measured in Newtons (N) in the SI.

We can calculate the weight (W) of an object of mass (m) using the equation:

W = mg

where g is the gravitational acceleration at the point where we want to calculate the weight. The bigger g is, the bigger the weight.