Density is calculated by dividing the mass of a specific unit by its volume. As mass is in the numerator, density increases as mass increases. Conversely, when the volume measurement in denominator increases, the density decreases.
When the mass of an object increases but the volume remains the same, the quantity of matter increases over a static volume, making the concentration of matter more dense. When the mass remains the same but the volume increases, the same amount of matter can spread out in a larger area, causing the object to become less dense. Density is most often measured using kilograms per cubic meter.