The mathematical equation for Boyle's law is:
where  denotes the pressure of the system,  denotes the volume of the gas,  is a constant value representative of the temperature and volume of the system.
So long as temperature remains constant the same amount of energy given to the system persists throughout its operation and therefore, theoretically, the value of  will remain constant. However, due to the derivation of pressure as perpendicular applied force and the probabilistic likelihood of collisions with other particles through collision theory, the application of force to a surface may not be infinitely constant for such values of , but will have a limit when differentiating such values over a given time. Forcing the volume  of the fixed quantity of gas to increase, keeping the gas at the initially measured temperature, the pressure  must decrease proportionally. Conversely, reducing the volume of the gas increases the pressure. Boyle's law is used to predict the result of introducing a change, in volume and pressure only, to the initial state of a fixed quantity of gas.
The initial and final volumes and pressures of the fixed amount of gas, where the initial and final temperatures are the same (heating or cooling will be required to meet this condition), are related by the equation:
Here  and  represent the original pressure and volume, respectively, and  and  represent the second pressure and volume.
Boyles law, Charless law, and Gay-Lussacs law form the combined gas law. The three gas laws in combination with Avogadros law can be generalized by the ideal gas law.