Compare gas effusion and diffusion rates with Graham’s law, from molar masses, plus relative effusion times.
Rate ratio
How to use this tool
In g/mol, e.g. H₂ ≈ 2.016, O₂ ≈ 31.998.
How many times faster gas 1 is, and the inverse time ratio.
In advanced options, to get gas 1’s absolute rate.
The lighter gas always wins.
Formula & worked example
Hydrogen (M ≈ 2) effuses 4 times faster than oxygen (M ≈ 32), and takes a quarter of the time.
Limitations — read this before you rely on it
Ideal-gas approximation at equal temperature and pressure; it breaks down for large openings, high pressures or strongly non-ideal gases.
Frequently asked questions
Gas escaping through a tiny hole into a vacuum; diffusion is mixing through another gas. Graham’s law approximates both.
Molecular speeds scale with 1/√M at a given temperature, from kinetic theory.
Both gases must be at the same temperature; the ratio itself is temperature-independent for ideal gases.
For large holes, high pressures or non-ideal gases, where bulk flow replaces molecular effusion.
Always the lighter one — rate is inversely proportional to √M.