There are many different ways to express density, and not using or converting into the proper units will result in an incorrect value. It is useful to carefully write out whatever values are being worked with, including units, and perform dimensional analysis to ensure that the final result has units of
mass
_____
volume
. Note that density is also affected by pressure and temperature. In the case of solids and liquids, change in density is typically low. However, when regarding gases, density is largely affected by temperature and pressure. An increase in pressure decreases volume, and always increases density. Increases in temperature tend to decrease density since volume will generally increase. There are exceptions however, such as water's density increasing between 0°C and 4°C