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Chemistry Tools · Updated October 21, 2026 · Reviewed by FormatFlow Editorial

Gas Partial Pressure Calculator

You can calculate the partial pressure of each gas in an ideal mixture from moles, from the individual partial pressures, or from mole fractions, using Dalton's law.

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At a glance

Works with
MIXTURE → PARTIAL
Processing
In your browser
Price
Free, no account
Updated
October 21, 2026
All Chemistry Tools

About Gas Partial Pressure Calculator

In a gas mixture, each gas contributes its own partial pressure, and the total pressure is the sum of those contributions. The share each gas carries is its mole fraction, so the composition of the mixture and the partial pressures describe the same thing.

This calculator works from any of the three common starting points: component moles and a total pressure, the individual partial pressures, or mole fractions and a total pressure. It shows the table of mole fractions and partial pressures, Dalton's law and every step.

What this tool does

The details that matter when you use Gas Partial Pressure Calculator for real work.

  • Three starting points

    Work from component moles, from the measured partial pressures, or from mole fractions with a total pressure; each mode checks its own inputs.

  • Mole fractions and partial pressures

    The table lists every gas with its mole fraction and partial pressure, and the summary gives the total pressure and component count.

  • Fraction normalization

    Mole fractions that do not add up to exactly 1 are normalized with a note, so a rounded composition still produces sensible partial pressures.

  • Pressure units

    Total and partial pressures can be entered and read in kPa, atm, bar or mmHg; conversions are handled internally through pascals.

  • Named components

    Give each gas an optional name such as N2 or O2 so the results table is easy to read and copy into a report.

  • Dalton's law steps

    The formulas for total pressure, mole fraction and partial pressure are printed alongside the substituted arithmetic for each gas.

How to use Gas Partial Pressure Calculator

No account, no installation — the whole job happens in this browser tab.
  1. 01

    Choose what is given

    Pick from moles, from partial pressures, or from mole fractions, depending on which quantities you already know.

  2. 02

    Enter the gas components

    Add a row for each gas with an optional name and its moles, partial pressure or mole fraction, using the same field for every row.

  3. 03

    Set the total pressure

    In the moles and fractions modes, enter the total pressure and pick its unit; in the partials mode the total is summed for you.

  4. 04

    Read the results table

    The table shows each gas with its mole fraction and partial pressure, and the summary states the total pressure and gas count.

  5. 05

    Check the working

    The step panel shows Dalton's law, the fraction calculation and the partial pressure substitution for every gas.

How this tool works

Works with
MIXTURE → PARTIAL
Processing
Client-side, in your browser. Nothing is uploaded.
Requirements
Chrome, Edge, Firefox or Safari · JavaScript enabled

Limitations worth knowing

  • Assumes an ideal, non-reacting gas mixture with all components at the same temperature and sharing the same volume.
  • Does not model real-gas fugacity or non-ideal mixture corrections, which matter at high pressure and near condensation.
  • Works with the composition data you enter; it does not measure or infer the composition of an unknown mixture.

Privacy and file handling

Gas names, moles, partial pressures and mole fractions are processed in your browser tab. Nothing is uploaded, stored or logged, and the calculator makes no network request.

Read the full privacy policy

Gas Partial Pressure Calculator FAQ

Short, direct answers to the questions people ask before using this tool.
What is Dalton's law of partial pressures?
Dalton's law says the total pressure of a non-reacting ideal gas mixture equals the sum of the partial pressures of its components. Each partial pressure is the pressure that gas would exert if it occupied the whole volume alone at the same temperature.
How do I calculate a partial pressure from moles?
Divide the gas's moles by the total moles to get its mole fraction, then multiply by the total pressure: P_i = (n_i / n_total) × P_total. For 0.20 mol of N2 in 0.50 mol total at 100 kPa, the fraction is 0.40 and the partial pressure is 40 kPa.
What is a mole fraction?
The mole fraction x_i is the number of moles of one component divided by the total moles of all components. It is dimensionless, lies between 0 and 1, and the mole fractions of all components add up to 1 for a complete mixture.
How do I find the total pressure from partial pressures?
Add the partial pressures of all the components: P_total = P_1 + P_2 + ... . For a mixture with partial pressures of 40 kPa and 60 kPa, the total pressure is 100 kPa and the mole fractions are 0.40 and 0.60.
Do the pressure units matter in the calculation?
Mole fractions are ratios, so they are unitless, but the partial pressures must be expressed in the same unit as the total pressure. This calculator converts every pressure through pascals and shows the results in the unit you selected.
Can mole fractions add up to something other than 1?
In a complete mixture they add up to 1, but rounded data may not. This calculator normalizes the fractions when the sum differs from 1 and shows a note, so the partial pressures still add up to the entered total pressure.
Does the partial pressure calculator work for real gases?
It uses the ideal gas model, which is accurate at moderate pressure and well above the condensation point. Real gases deviate at high pressure or low temperature, and fugacity rather than partial pressure is used in rigorous non-ideal treatments.
Do temperature and volume affect the partial pressures?
For a fixed composition and total pressure, the partial pressure is set by the mole fraction, so temperature and volume do not enter the Dalton's law step directly. They matter through the total pressure, which follows from the amount of gas, temperature and volume.

Background reading

Format guides that explain the trade-offs behind Gas Partial Pressure Calculator.