Partial Pressure Calculator

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Dalton's law is the classic Pᵢ = Xᵢ × P_total. The ideal gas law lets you find partial pressure from moles, temperature, and volume. Henry's law relates dissolved gas to its partial pressure above a liquid.
All pressure inputs and outputs use this unit.
Fraction of total moles that this component contributes, between 0 and 1. Dry-air oxygen is about 0.21, nitrogen about 0.78.
The combined pressure of the entire gas mixture.
atm
Enter the mole fractions of up to three additional components and see all their partial pressures at once.
Partial pressure (Pᵢ)
0.21
Pressure of all other components0.79
Partial pressure (kPa)21.278
Partial pressure (mmHg)159.6
This component0.21
All other components0.79

Partial pressure = 0.21 atm

  • This component makes up 21% of the moles in the mixture and therefore 21% of the total pressure.
  • The remaining components together hold 0.79 atm.
  • Dalton's law assumes ideal behaviour: no intermolecular forces, so partial pressures add directly to 1 atm.
  • Equivalent: 21.28 kPa / 159.6 mmHg (0.21 atm).

Next stepRepeat for each component; all mole fractions must sum to 1 and all partial pressures to the total.

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