Gas Mixture & Partial Pressure Calculator
xᵢ = valueᵢ / Σ value, P(total) = Σ Pᵢ
Composition of a gas mixture from ratios, mol%, vol%, flows or partial pressures (Dalton's law).
Gas mixture
Gas mixture
N2 / O2 = 78 / 22 vol%
N2:O2 = 3.55:1
N2 = 78% · O2 = 22%
Total: 100 vol%
Result
N2 78% · O2 22%
Total 100 vol%.
Calculation
Volume percent total
total = Σ valueᵢ
100 %
Fraction of N2
xᵢ = valueᵢ / Σ value
78 / 100
78 %
Fraction of O2
xᵢ = valueᵢ / Σ value
22 / 100
22 %
Ratio
N2:O2 = 3.55:1
Inputs
- N2
- 78 vol%
- O2
- 22 vol%
Composition is calculated from the values you entered; no carrier gas, balance gas or standard atmosphere is assumed.
Mole % and volume % are only equal for ideal gases. At elevated pressure or near condensation, real-gas behaviour makes them differ — the basis you selected is preserved throughout and never silently converted.
Flow-based fractions assume all flows are at the same reference conditions (for sccm / SLPM, standard temperature and pressure as defined by your mass-flow controller).
Composition
- N278 vol%78.00%
- O222 vol%22.00%
Ratio — N2:O2 = 3.55:1
About this calculator
Define your gas atmosphere the way you know it — as a ratio, volume or mole percent, mass-flow rates, or partial pressures — and this calculator derives the full composition: each component's fraction, the total, and the simplified ratio. Units of the same physical quantity (for example sccm and SLPM, or bar and mbar) are converted to a common reference before summing.
For partial pressures, Dalton's law applies: the total pressure is the sum of the partial pressures and each mole fraction is Pᵢ / P(total). For percentage bases, the calculator reports the deviation from 100% without silently correcting it, so typos in your recipe stay visible.
Mole % and volume % are equal only for ideal gases, and flow-based fractions assume all flows reference the same standard conditions (as defined by your mass-flow controllers). Nothing is converted between these bases automatically — the basis you select is preserved throughout.
LabReadyTools is provided as a calculation aid. Users remain responsible for verifying calculations, units, chemical compatibility, experimental procedures and applicable safety requirements before laboratory use.