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Ideal Gas Law

The ideal gas law is used to relate the density, pressure, and temperature of a gas. By using the ideal gas law, an approximation of a real gas would be made. To view the ideal gas law, refer to equation 1.

(Eq 1) $ρ=\frac{P}{RT}$

ρ = Density

P = Pressure

R = Gas Constant

T = Temperature

When using the ideal gas law the value for pressure is the absolute pressure. This means atmospheric pressure would have to be considered as well as gage pressure. Refer to equation 2.

(Eq  2) $P{abs}=P{atm}+P{gage}$

The temperature value T also has to be an absolute value. This means that the temperature has to be in Kelvin (equation 3) for SI units or Rankin for English units (equation 4).

(Eq 3) $T_{Kelvin}=T_{Celsius}+273$

(Eq 4) $T_{Rankin} = T_{Fahrenheit}+460$

Finally, the R value seen in the ideal gas law represents the gas constant. Refer to the table below to view gas constants for different gases.



Gas Constant

English Units


Gas Constant

SI Units


Air (Standard) 1.716 X 103 2.869 X 102
Carbon Dioxide 1.130 X 103 1.889 X 102
Helium 1.242 X 104 2.077 X 103
Hydrogen 2.466 X 104 4.124 X 103
Methane 3.099 X 103 5.183 X 102
Nitrogen 1.775 X 103 2.968 X 102
Oxygen 1.554 X 103 2.598 X 102


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