Gas Specific Gravity Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 26, 2026Gas Specific Gravity Calculator
Whether a leaked gas rises and disperses or sinks and pools at floor level is a genuine safety question with a precise numerical answer: specific gravity relative to air.
Formula: SG = Mgas / Mair, using Mair = 28.97 g/mol
Example: methane (16.04 g/mol) has a specific gravity of about 0.55 - noticeably lighter than air, which is exactly why methane/natural gas leaks tend to rise and disperse rather than pool.
Frequently Asked Questions
Why does this matter for gas detector placement?
Detectors for lighter-than-air gases (like methane, SG below 1) are typically mounted high, while detectors for heavier-than-air gases (like propane, SG around 1.5, or CO2) are mounted low, since each gas naturally accumulates in a different part of a room.
Is specific gravity the same as density?
Not quite - specific gravity is a dimensionless ratio relative to air, while density has actual units (like kg/m³) - specific gravity is more convenient for quick safety comparisons since it does not depend on the ambient pressure and temperature the way absolute density does.