1. Mass: The mass of an object is the amount of matter it contains. The more matter an object has, the denser it will be.

2. Volume: The volume of an object is the amount of space it takes up. The less space an object takes up, the denser it will be.

Density is calculated by dividing the mass of an object by its volume. The units for density are kilograms per cubic meter (kg/m³).