How this calculator works
Combine pV = nRT with n = m/M. Use absolute pressure and thermodynamic temperature; Celsius and Fahrenheit selections convert to kelvin. R = 8.31446261815324 J mol^-1 K^-1 follows from exact SI constants in CODATA 2022. Real gases may require a compressibility factor, especially at high pressure or near condensation.
Formula
M = mRT/(pV); n = pV/(RT), with SI pressure, volume and temperature.
Worked example
A 28 g sample at 300 K occupying 0.02494338785445972 m3 at 100 kPa has M = 28 g/mol and n = 1 mol. Twice that mass at the same conditions gives 56 g/mol.
Advertisement
Frequently asked questions
Can I enter gauge pressure?
Add ambient pressure first. The ideal gas law requires absolute pressure.
What if the gas was collected over water?
Subtract water vapour partial pressure to obtain the dry-gas pressure.
Can I change the gas constant?
The SI constant is fixed here; changing units is handled by the selectors.