Ideal Gas Law
PV = nRT
P is the pressure of gas in pascals; V the volume it occupies in cubic meters; T the temperature of the gas in degrees Kelvin; n is the molar mass of the gas occupying the volume V; R is the gas constant
R = 0.0821 or 8.314
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.