Chemistry calculator

Combined Gas Law Calculator

Solve for initial or final pressure, volume, or temperature using P₁V₁/T₁ = P₂V₂/T₂, with automatic unit conversion.

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Solve the combined gas law

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Calculator guide

How this calculator works

Combined Gas Law Calculator determines the relationship between pressure, volume, and temperature of a gas when the amount of gas remains constant. It helps chemistry students, researchers, and laboratory professionals calculate unknown gas properties using the combined gas law equation.

Formula explanation

The combined gas law connects pressure, volume, and temperature changes for a fixed amount of gas.

Formula

Combined Gas Law: P₁V₁/T₁ = P₂V₂/T₂

Worked example

Example: Initial and final gas conditions can be used to calculate an unknown variable.

Assumptions

  • The amount of gas remains constant.
  • Temperature values use an absolute temperature scale.
  • The gas behaves approximately as an ideal gas.
  • Pressure and volume units remain compatible.

Examples

  • Example: Calculate final pressure when gas volume and temperature change while the amount of gas stays constant.
  • Example: Scientists use the combined gas law to predict gas behavior under changing laboratory conditions.

Common mistakes

  • Mixing temperature scales.
  • Using inconsistent units.
  • Applying the formula to changing gas amounts.

Variables

  • Initial pressure
  • Initial volume
  • Initial temperature
  • Final pressure
  • Final volume
  • Final temperature
  • Constant amount of gas assumption

Limitations

  • Accuracy decreases when gases do not behave like ideal gases.
  • The calculation applies only when the amount of gas remains constant.

Scientific references

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

Content review

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

Applications

  • Gas behavior analysis
  • Chemistry education
  • Laboratory calculations
  • Scientific experiment planning

Frequently asked questions

How is the combined gas law calculated?

The combined gas law is calculated by comparing the pressure, volume, and temperature ratios between two different gas conditions.

What does the combined gas law describe?

The combined gas law describes how pressure, volume, and temperature are related for a fixed amount of gas.

Why must temperature be converted to Kelvin?

Kelvin is required because gas law calculations use an absolute temperature scale.

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

Gas-law guide

What is the combined gas law?

The combined gas law describes how the pressure, volume, and absolute temperature of a fixed amount of gas change between two states.

It combines Boyle's law, Charles's law, and Gay-Lussac's law into one equation.

Core equation

Combined gas law formula

P₁V₁/T₁ = P₂V₂/T₂
  • P₁ and P₂ are initial and final pressure.
  • V₁ and V₂ are initial and final volume.
  • T₁ and T₂ are initial and final absolute temperature.

Solve any variable

Rearranged combined gas law equations

  • P₂ = P₁V₁T₂ ÷ (V₂T₁)
  • V₂ = P₁V₁T₂ ÷ (P₂T₁)
  • T₂ = P₂V₂T₁ ÷ (P₁V₁)
  • P₁ = P₂V₂T₁ ÷ (V₁T₂)
  • V₁ = P₂V₂T₁ ÷ (P₁T₂)
  • T₁ = P₁V₁T₂ ÷ (P₂V₂)

Worked example

Calculate final gas volume

A gas starts at 1 atm, 2 L, and 300 K. It changes to 0.8 atm and 450 K. Find the final volume.

  1. Use V₂ = P₁V₁T₂ ÷ (P₂T₁).
  2. Substitute V₂ = 1 × 2 × 450 ÷ (0.8 × 300).
  3. Calculate the result: V₂ = 3.75 L.

Supported units

Pressure, volume, and temperature units

  • Pressure: Pa, kPa, bar, atm, and mmHg.
  • Volume: cubic meters, liters, and milliliters.
  • Temperature: Kelvin, Celsius, and Fahrenheit.
  • The answer is returned in the selected unit for the unknown variable.

Correct usage

When to use the combined gas law

  • The amount of gas remains fixed.
  • Pressure, volume, or temperature changes between two states.
  • Temperatures are interpreted on an absolute scale.
  • The gas behaves approximately as an ideal gas.

Related calculators

Questions and answers

Calculator FAQ

How is the combined gas law calculated?

The combined gas law is calculated by comparing the pressure, volume, and temperature ratios between two different gas conditions.

What does the combined gas law describe?

The combined gas law describes how pressure, volume, and temperature are related for a fixed amount of gas.

Why must temperature be converted to Kelvin?

Kelvin is required because gas law calculations use an absolute temperature scale.