In Physics, mass is both the amount of matter in an object and its resistance to acceleration from a net force. The mass project of an object determines its gravitational attraction to another object.
Mass is not the same as weight. This is because mass is an independent property, whereas weight is a force created by gravitational attraction to another object. For example, A kilogram of iron would not weigh the same on the surface of Mars as it does here on Earth but it would still have the same mass.
It is often the case that mass correlates with size, though the tremendous diversity of matter in the universe means you can have tiny objects that are much more massive than larger ones.
How to Calculate Mass
To calculate mass, multiply the density by the volume of the object.
m = ρ x V
In the equation above, ρ is density, V is volume and m is the result in cubed units.