Chemistry calculator

Dalton's Law Calculator

Calculate the total pressure of a gas mixture or find a missing partial pressure using Ptotal = P₁ + P₂ + ⋯ + Pₙ, with automatic pressure-unit conversion.

Enter gas pressures

Solve Dalton's law

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Gas components

Partial pressures

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Calculator guide

How this calculator works

Dalton's Law Calculator determines the total pressure of a gas mixture by calculating the sum of individual partial pressures. It helps chemistry students, researchers, and laboratory professionals analyze gas mixtures using Dalton's Law of Partial Pressures.

Formula explanation

Dalton's law calculates total gas pressure by adding the partial pressures of individual gases.

Formula

Dalton's Law: P(total) = P₁ + P₂ + P₃ + ... + Pₙ

Worked example

Example: Total pressure equals the sum of all individual gas partial pressures.

Assumptions

  • Each gas contributes independently to total pressure.
  • Gas components behave approximately as ideal gases.
  • All pressure values use compatible units.

Examples

  • Example: Calculate total pressure by adding the partial pressures of multiple gases in a container.
  • Example: Researchers use Dalton's Law to analyze the composition and pressure of gas mixtures.

Common mistakes

  • Adding incompatible pressure units.
  • Ignoring individual gas contributions.
  • Confusing partial and total pressure.

Variables

  • Individual gas partial pressures
  • Total pressure of gas mixture
  • Number of gas components
  • Compatible pressure units

Limitations

  • Accuracy decreases when gases significantly deviate from ideal gas behavior.
  • The law assumes gases in the mixture act independently.

Scientific references

  • OpenStax Chemistry: Gas Mixtures
  • NIST Chemistry Reference Data
  • Scientific gas measurement guidelines

Content review

Reviewed by: ScienceCalcHub Chemistry Review Team | Last reviewed: 2026-08-30

Applications

  • Gas mixture analysis
  • Chemistry education
  • Laboratory gas calculations
  • Industrial and scientific research

Frequently asked questions

How is Dalton's Law calculated?

Dalton's Law is calculated by adding the partial pressures of all gases present in a mixture to determine the total pressure.

What does Dalton's Law describe?

Dalton's Law describes how each gas in a mixture contributes independently to the overall pressure of the mixture.

What units can be used for Dalton's Law?

Any compatible pressure units can be used as long as all pressure values are expressed in the same unit system.

Accuracy and transparency

Created and maintained by our editorial team

This chemistry calculator is maintained by the ScienceCalcHub Editorial Team. Its calculation logic is tested with representative inputs, while the supporting guidance is checked for formula clarity, units, assumptions, and common mistakes.

Written by
ScienceCalcHub Editorial Team
Reviewed by
ScienceCalcHub Scientific Review Team
Review standard
Formula accuracy, units, examples, and educational clarity

Learn more about our formula-review and correction process, explore our calculation methodology, or view our scientific references.

  • Calculation logic tested
  • Variables and units explained
  • Assumptions stated clearly
  • Corrections handled transparently

Partial-pressure guide

What is Dalton's law?

Dalton's law of partial pressures describes the pressure produced by a mixture of nonreacting gases. The total pressure equals the sum of the partial pressure contributed by every gas.

Each gas behaves as though it occupies the container independently. Its partial pressure contributes to the measurable pressure of the complete mixture.

Core equation

Dalton's law formula

Ptotal = P₁ + P₂ + ⋯ + Pₙ
  • Ptotal is the total pressure of the gas mixture.
  • P₁, P₂, and Pₙ are the individual partial pressures.
  • All pressures must use compatible units before they are added.

Find an unknown pressure

Missing partial pressure formula

Pmissing = Ptotal − (P₁ + P₂ + ⋯ + Pₙ)

Add the known partial pressures and subtract their sum from the measured total pressure. A valid total pressure must exceed the combined known partial pressures.

Worked example

Calculate total pressure

A gas mixture contains nitrogen at 0.78 atm, oxygen at 0.21 atm, and other gases at 0.01 atm. Find its total pressure.

  1. Write the equation: Ptotal = P₁ + P₂ + P₃.
  2. Substitute the pressures: Ptotal = 0.78 + 0.21 + 0.01 atm.
  3. Add the values: Ptotal = 1.00 atm.

Missing-gas example

Calculate a missing partial pressure

A mixture has a total pressure of 760 mmHg. Two known gases contribute 300 mmHg and 250 mmHg.

  1. Add known pressures: 300 + 250 = 550 mmHg.
  2. Subtract from the total: 760 − 550 = 210 mmHg.
  3. The missing partial pressure is 210 mmHg.

Supported units

Dalton's law pressure units

  • Pascals (Pa)
  • Kilopascals (kPa)
  • Bar
  • Atmospheres (atm)
  • Millimeters of mercury (mmHg)

Mixed units are converted to pascals internally. The final value is then converted to the result unit you select.

Practical applications

Where Dalton's law is used

  • Analyzing atmospheric and laboratory gas mixtures.
  • Correcting gas pressure collected over water.
  • Understanding breathing and respiratory gas exchange.
  • Planning compressed-air and diving gas mixtures.
  • Solving chemistry and ideal-gas problems.

Gas collected over water

Correct pressure for water vapor

Gas collected over water contains both the desired gas and water vapor. Subtract the water-vapor pressure from the total measured pressure:

Pgas = Ptotal − Pwater vapor

Water-vapor pressure depends on temperature, so use a reliable vapor pressure table for the experiment's measured temperature.

Calculation limits

Assumptions and common mistakes

  • Convert incompatible pressure units before adding values.
  • Include every gas present in the mixture.
  • Use positive pressure values.
  • Do not confuse partial pressure with mole fraction.
  • Expect deviations for strongly interacting or nonideal gases.

Related tools

Use the Ideal Gas Law Calculator when pressure, volume, moles, and temperature are involved.

Use the Combined Gas Law Calculator when pressure, volume, and temperature change between two gas states.

Use the Gay-Lussac's Law Calculator for pressure-temperature changes at constant volume.

Questions and answers

Calculator FAQ

How is Dalton's Law calculated?

Dalton's Law is calculated by adding the partial pressures of all gases present in a mixture to determine the total pressure.

What does Dalton's Law describe?

Dalton's Law describes how each gas in a mixture contributes independently to the overall pressure of the mixture.

What units can be used for Dalton's Law?

Any compatible pressure units can be used as long as all pressure values are expressed in the same unit system.