The **universal gas equation**, or **ideal gas law**, is an equation of state of an ideal gas:

*pV*=*nRT*

The equation is valid only for an ideal gas. Real gases obey this equation only approximately, but its validity increases as the density of the gas tends to zero.

The picture shows some isotherms of an ideal gas (i.e. the relation between pressure p and volume V at fixed temperature T; plotted for a set of temperatures, with increasing T from lower to upper curve):

See also: