Boyles law, also referred to as the Boyle–Mariotte law or Mariottes law (especially in France), is an empirical gas law that describes the relationship between pressure and volume of a confined gas. Boyle's law has been stated as:
Mathematically, Boyle's law can be stated as:
or
where  is the pressure of the gas,  is the volume of the gas, and  is a constant.
Boyle's law states that when the temperature of a given mass of confined gas is constant, the product of its pressure and volume is also constant. When comparing the same substance under two different sets of conditions, the law can be expressed as:
showing that as volume increases, the pressure of a gas decreases proportionally, and vice versa. 
Boyle's law is named after Robert Boyle, who published the original law in 1662. An equivalent law is Mariotte’s law named after French physicist Edme Mariotte.