The three gas laws that laid the foundation for the ideal gas law are as follows:
Boyle's law: At constant temperature, the volume of a gas is inversely proportional to its pressure.
Charles's law: At constant pressure, the volume of a gas is proportional to the absolute temperature.
GayLussac's law: At constant volume, the pressure of a gas is proportional to its temperature.
The combined gas law combines these laws and summarizes the relationship between thermodynamic variables (volume $V$, pressure $p$, and absolute temperature $T$):
$\frac{{p}_{1}{V}_{1}}{{T}_{1}}\=\frac{{p}_{2}{V}_{2}}{{T}_{2}}$.
Note that the temperature is absolute, so it must be expressed in Kelvin (K) as opposed to Celsius ($\xb0$C) or Fahrenheit ($\xb0$F) for the equation to hold numerically. Typically, experiments are conducted at standard pressure and temperature, 101.3 kPa and 25°C. It is important to note that sometimes volume, pressure and temperature are expressed in terms of nonstandard units. The following table contains conversions to SI units:
$\mathbf{Non}\mathbf{}\mathbf{Standard}\mathbf{}\mathbf{Unit}$

$\mathbf{SI}\mathbf{}\mathbf{Unit}$

$\mathrm{Pressure}$

$1\mathrm{atm}$

$101.3\mathrm{kPa}$

$1\mathrm{torr}$

$133.3\mathrm{kPa}$

$\mathrm{Temperature}$

$0\xb0\mathrm{C}$

$273\mathrm{K}$

$0\xb0\mathrm{F}$

$255.4\mathrm{K}$



