Chemistry calculator

Gay-Lussac's Law Calculator

Calculate initial or final gas pressure and temperature using P₁/T₁ = P₂/T₂, with automatic pressure and temperature unit conversion.

Enter three known values

Solve Gay-Lussac's law

Free tool

The gas volume before the temperature change.

The gas temperature before the change.

This is the value being calculated.

The gas temperature after the change.

Gay-Lussac's law assumes a fixed amount of gas in a rigid container at constant volume. Temperatures are converted internally to Kelvin and must remain above absolute zero.

Try an example:

Result

Your result will appear here

Select the variable to calculate, enter the other three values, and choose the volume and temperature units.

Calculator guide

How this calculator works

Gay-Lussac's Law Calculator determines the relationship between gas pressure and temperature when volume remains constant. It helps chemistry students, researchers, and laboratory professionals calculate unknown pressure or temperature values using Gay-Lussac's Law.

Formula explanation

Gay-Lussac's law calculates the relationship between gas pressure and temperature when volume remains constant.

Formula

Gay-Lussac's Law: P₁/T₁ = P₂/T₂

Worked example

Example: Increasing gas temperature increases pressure in a sealed container.

Assumptions

  • Volume remains constant during the calculation.
  • Temperature values are converted to absolute temperature units.
  • The gas behaves approximately as an ideal gas.

Examples

  • Example: Calculate final pressure when gas temperature changes inside a fixed-volume container.
  • Example: Scientists use Gay-Lussac's Law to study pressure-temperature relationships in controlled experiments.

Common mistakes

  • Using Celsius temperatures.
  • Ignoring constant volume.
  • Incorrect pressure conversions.

Variables

  • Initial pressure
  • Initial temperature
  • Final pressure
  • Final temperature
  • Constant volume assumption

Limitations

  • Accuracy decreases when gases do not behave like ideal gases.
  • The relationship applies only when volume 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 pressure analysis
  • Chemistry education
  • Laboratory gas calculations
  • Scientific experiments

Frequently asked questions

How is Gay-Lussac's Law calculated?

Gay-Lussac's Law is calculated by comparing the ratio between gas pressure and absolute temperature before and after a temperature change.

What does Gay-Lussac's Law describe?

Gay-Lussac's Law describes the direct relationship between gas pressure and absolute temperature when volume remains constant.

Why is Kelvin used for temperature?

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 Gay-Lussac's law?

Gay-Lussac's law describes how the pressure of a fixed amount of gas changes with absolute temperature when volume remains constant. Heating the gas raises its pressure, while cooling lowers it.

Pressure and absolute temperature are directly proportional. Doubling the Kelvin temperature doubles the pressure under the required conditions.

Core equation

Gay-Lussac's law formula

P₁/T₁ = P₂/T₂
  • P₁ is the initial gas pressure.
  • T₁ is the initial absolute temperature.
  • P₂ is the final gas pressure.
  • T₂ is the final absolute temperature.

Celsius and Fahrenheit inputs are converted to Kelvin before the pressure-temperature ratio is evaluated.

Solve any variable

Rearranged Gay-Lussac's law equations

  • Final pressure: P₂ = P₁ × T₂ ÷ T₁
  • Initial pressure: P₁ = P₂ × T₁ ÷ T₂
  • Final temperature: T₂ = T₁ × P₂ ÷ P₁
  • Initial temperature: T₁ = T₂ × P₁ ÷ P₂

Select the unknown variable, enter the remaining values, and choose the required pressure and temperature units.

Worked example

Calculate gas pressure after heating

A sealed rigid container holds gas at 1 atm and 300 K. The gas is heated to 450 K. Find the final pressure.

  1. Write the equation: P₁/T₁ = P₂/T₂.
  2. Rearrange it: P₂ = P₁ × T₂ ÷ T₁.
  3. Substitute values: P₂ = 1 atm × 450 K ÷ 300 K.
  4. Calculate the result: P₂ = 1.5 atm.

The Kelvin temperature increases by a factor of 1.5, so pressure also increases by a factor of 1.5.

Supported units

Pressure and temperature units

  • Pressure: pascals, kilopascals, bar, atmospheres, and millimeters of mercury.
  • Temperature: Kelvin, Celsius, and Fahrenheit.
  • Mixed pressure units are converted internally before solving.
  • The result uses the selected output unit.

Required conditions

When Gay-Lussac's law applies

  • Gas volume remains constant.
  • The amount of gas remains fixed.
  • The container is sealed and rigid.
  • Temperature is interpreted on an absolute scale.
  • The gas behaves approximately as an ideal gas.

Direct relationship

Understanding the pressure-temperature graph

A graph of gas pressure against Kelvin temperature forms a straight line when volume and the amount of gas remain constant.

This linear relationship means equal proportional changes in absolute temperature produce equal proportional changes in pressure.

Calculation limits

Important limitations and mistakes

  • Never substitute Celsius or Fahrenheit directly into the temperature ratio.
  • Do not apply the law if container volume changes significantly.
  • Pressure values must exceed zero.
  • Temperatures must remain above absolute zero.
  • Real gases can depart from ideal behavior at high pressure or near condensation.

Related tools

Use the Boyle's Law Calculator when pressure and volume change at constant temperature.

Use the Charles's Law Calculator when volume and temperature change at constant pressure.

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

Questions and answers

Calculator FAQ

How is Gay-Lussac's Law calculated?

Gay-Lussac's Law is calculated by comparing the ratio between gas pressure and absolute temperature before and after a temperature change.

What does Gay-Lussac's Law describe?

Gay-Lussac's Law describes the direct relationship between gas pressure and absolute temperature when volume remains constant.

Why is Kelvin used for temperature?

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