Gas Density Calculator
If you're searching for how to calculate the density of a gas, you're in the right place! Input the gas constant (or the molar mass), pressure, and temperature, and this density calculator will find the answer. You can use this tool to calculate the density of fuel gases, such as propane and methane (the main component of natural gas).
In the following sections, we talk about the density of a gas and the formulas for its calculation.
The density of a gas
The density of liquids and solids is approximately constant, but we can't say the same for gases. For gases, density is highly dependent on temperature and pressure, and we can study that dependence using the ideal gas law:
, where:
 $p$  Absolute pressure of the gas, in pascals (Pa);
 $V$  Volume occupied by the gas in cubic meters (m^{3});
 $n$  Number of moles in mol;
 $R$  Universal gas constant, whose value is 8.3144626 J/(mol K); and
 $T$  Absolute temperature of the gas, in kelvin (K).
As the mass of a gas equals the number of moles times its molar mass ($m = nM$ or $n = \frac{m}{M}$), we can express the ideal gas law as:
where $M$ is the molar mass, in g/mol or kg/mol.
Density equals mass divided by volume. Therefore, solving for $m/V$ in the previous equation results in the following gas density formula:
That's how we calculate the density of gases if we know the molar mass ($M$). If we know the specific gas constant of the substance instead of $M$, we can calculate the gas density with the following formula:
where $R_s$ is the specific gas constant of the substance, in J/kg K.
How to calculate gas density
In summary, we have two formulas to calculate gas density:

If we know the molar mass of the substance, we calculate the gas density with $\rho = Mp/\bar{R}T$, where:
 $\rho$ — Gas density, in kg/m³;
 $M$ — Molar mass, in kg/mol or g/mol;
 $p$ — Pressure, in Pa;
 $\bar{R}$ — Universal gas constant, whose value is 8.3144626 J/(mol K);
 $T$ — Temperature, in kelvin (K);

If we know the specific gas constant of the substance, we use this gas density formula $\rho = p/R_\text{s} T$, where $R_s$ is the specific gas constant, in J/kg K.
The density of various ideal gases at 1 atm and 15°C
If you know the gas is at 1 atm and 15°C, you don't need to deal with pressure and temperature to calculate the density. You can look at the following density values of gases at 1 atm and 15°C:
 Air: 1.2252 kg/m³
 Argon: 1.6898 kg/m³
 Butane: 2.454 kg/m³
 Carbon dioxide: 1.8615 kg/m³
 Carbon monoxide: 1.1848 kg/m³
 Ethane: 1.2718 kg/m³
 Ethylene: 1.1864 kg/m³
 Helium: 0.1693 kg/m³
 Hydrogen: 0.08527 kg/m³
 Methane: 0.6786 kg/m³
 Neon: 0.8537 kg/m³
 Nitrogen: 1.1848 kg/m³
 Octane: 4.824 kg/m³
 Oxygen: 1.3535 kg/m³
 Propane: 1.8655 kg/m³
 Steam: 0.1878 kg/m³