Vapor Density Calculator
Enter a molar mass to get vapor density vs. air, or add temperature and pressure for absolute density via the ideal gas law.
Common Gases — Click to Fill
Enter the molar mass or click a gas above.
Vapor Density = Molar Mass ÷ 28.97. Values >1 sink; >2.5 pool hazard.
Relative Vapor Density vs Air
Enter a molar mass to see results.
—
vs air
Lighter than air
Heavier than air
0
1 (air)
2.5
4+
- Gas molar mass
- —
- Air molar mass
- 28.97 g/mol
Summary
Enter a molar mass to get vapor density vs. air, or add temperature and pressure for absolute density via the ideal gas law.
How it works
- Relative vapor density = molar mass of gas ÷ 28.97 (molar mass of air).
- Absolute density uses the ideal gas law: ρ = (P × M) / (R × T), where P is pressure in Pa, M is molar mass in kg/mol, R = 8.314 J/(mol·K), and T is temperature in Kelvin.
- Temperature inputs in °C are converted to Kelvin by adding 273.15.
- Pressure inputs in atm or mmHg are converted to Pa before calculation.
Use cases
- Assess flammable gas pooling hazard in safety engineering and process design.
- Size ventilation systems for spaces that handle heavier-than-air gases.
- Estimate gas behavior in chemical process equipment at operating conditions.
- Verify stoichiometric calculations involving gas densities in laboratory settings.
Frequently Asked Questions
Last updated: 2026-06-18 ·
Reviewed by Nham Vu