Free · Thermodynamics calculators 🌡️

Ideal-Gas Density, Pressure & Molar Mass

Relate ideal-gas density to absolute pressure, absolute temperature and molar mass, with paired mass and mole units.

  • Formula & worked example
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

At 300 K, pressure 2,494.338785445972 Pa and molar mass 20 g/mol give an ideal-gas density of 0.02 kg/m³.

Density = absolute pressure × molar mass / (R × absolute temperature)

Worked example

Enter these known values and leave the other values blank.

Absolute gas pressure
2494.338785445972 Pa
Gas temperature
300 K
Molar mass of gas
20 g / mol
Ideal-gas mass density
0.02 kg/m³

Assumptions and limitations

  • The model assumes ideal-gas behavior. Dense gases, high pressures, phase changes and strong intermolecular interactions can require a real-gas equation.
  • Pressure must be absolute, not gauge pressure. Temperature is converted to kelvins internally and must be above absolute zero.
  • Molar mass is mass per mole; for a mixture, use the mixture’s mean molar mass. R is 8.31446261815324 J/(mol·K).

Common questions

Can I enter Celsius or Fahrenheit?

Yes. Select the matching temperature unit. The equation uses its absolute kelvin equivalent.

Can I enter a pressure gauge reading directly?

Add the relevant ambient absolute pressure first. The ideal-gas equation requires total absolute pressure.

References

Pounds-force per square inch use the exact international pound and inch with standard gravity, replacing the rounded captured factor. Bookify uses exact customary mass and volume definitions for density units, replacing rounded factors in the reference.

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