What this calculator does
Molar mass of a gas works out finds a gas’s molar mass from its mass, pressure, volume and temperature (ideal gas law). Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
Formulan = PV / RT, then M = m / n (R = 0.0821 L·atm/(mol·K))
The inputs explained
| Field | What to enter |
|---|---|
| Mass of gas (g) | A number, measured in g. Starts at 1.25. |
| Pressure (atm) | A number, measured in atm. Starts at 1. |
| Volume (L) | A number, measured in L. Starts at 1. |
| Temperature (K) | A number, measured in K. Starts at 273.15. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with mass of gas
Every other input is held at the calculator’s starting values while mass of gas varies. Select any row to load that scenario into the calculator.
How the answer changes with mass of gas
| Mass of gas (g) | Molar mass | Moles of gas (n = PV/RT) | Note |
|---|---|---|---|
| 0.63 | 14.13 g/mol | 0.0446 mol | Assumes ideal-gas behaviour; real gases deviate at high pressure or low temperature. |
| 0.94 | 21.08 g/mol | 0.0446 mol | Assumes ideal-gas behaviour; real gases deviate at high pressure or low temperature. |
| 1.25 | 28.03 g/mol | 0.0446 mol | Assumes ideal-gas behaviour; real gases deviate at high pressure or low temperature. |
| 1.88 | 42.16 g/mol | 0.0446 mol | Assumes ideal-gas behaviour; real gases deviate at high pressure or low temperature. |
| 2.5 | 56.06 g/mol | 0.0446 mol | Assumes ideal-gas behaviour; real gases deviate at high pressure or low temperature. |
| 3.75 | 84.10 g/mol | 0.0446 mol | Assumes ideal-gas behaviour; real gases deviate at high pressure or low temperature. |