Enter mixture data
Dalton’s law and supporting equations
Dalton’s Law: Ptotal = ΣPi
Partial pressure from mole fraction: Pi = xi × Ptotal
Mole fraction from moles: xi = ni / ntotal
Ideal gas total pressure: Ptotal = (ntotalRT) / V
Ideal gas partial pressure: Pi = (niRT) / V
Where P is pressure, x is mole fraction, n is amount in moles, R is the gas constant, T is absolute temperature, and V is mixture volume.
Steps
- Select the calculation method that matches your available data.
- Enter total pressure if you already know the mixture pressure.
- Choose fraction mode for composition ratios or mole mode for gas amounts.
- Use the ideal gas method when moles, temperature, and volume are known.
- Add or remove gas rows as needed for the mixture.
- Pick output pressure units and decimal precision.
- Click the calculate button to show results above the form.
- Review the table, chart, and export the results as CSV or PDF.
Simple air-style mixture at 1 atm
| Gas | Mole Fraction | Share (%) | Partial Pressure (atm) | Partial Pressure (kPa) |
|---|---|---|---|---|
| Nitrogen | 0.7800 | 78.00 | 0.7800 | 79.03 |
| Oxygen | 0.2100 | 21.00 | 0.2100 | 21.28 |
| Argon | 0.0100 | 1.00 | 0.0100 | 1.01 |
| Total | 1.0000 | 100.00 | 1.0000 | 101.33 |
Common questions
1) What does Dalton’s law state?
Dalton’s law says the total pressure of a nonreacting gas mixture equals the sum of each component’s partial pressure. Each gas behaves as if it alone occupied the container.
2) When should I use fraction mode?
Use fraction mode when you already know the mixture composition as mole fractions or percentages and you also know total pressure. The calculator multiplies each fraction by total pressure.
3) When should I use mole mode?
Use mole mode when you know total pressure and each gas amount in moles. The calculator first finds each mole fraction, then converts those fractions into partial pressures.
4) Why does the ideal gas method need temperature and volume?
That method uses the ideal gas equation. Temperature and volume are required to calculate total pressure from the gas amounts before each component pressure is determined.
5) Are partial pressure and mole fraction always proportional?
Yes, for ideal gas mixtures under Dalton’s law, a component’s pressure share matches its mole fraction. A gas with 25% mole fraction contributes 25% of total pressure.
6) What happens if my fractions do not sum to one?
You can correct the entries manually or enable automatic normalization. Normalization rescales every fraction proportionally so the mixture total becomes exactly one.
7) Which pressure unit should I choose?
Choose the unit that matches your lab, classroom, or engineering workflow. The calculator converts internally, so results remain consistent across atm, kPa, bar, psi, and more.
8) Can this calculator handle reactive mixtures?
No. This tool assumes a nonreacting mixture and applies Dalton’s law directly. Reactive systems may change composition, temperature, or total pressure during the process.