Combined Gas Law Calculator
Calculate the final state of a fixed amount of gas as its pressure, volume, or temperature changes. Enter the known values in the calculator to find the unknown variable.
Combined gas law
Find the final pressure when volume and temperature change.
Enter positive values. Temperatures must be in Kelvin and pressures must be absolute, not gauge pressure.
Your answer will appear here
Enter your known values and select Calculate to see the result, formula, and solution steps.
How the combined gas law works
The combined gas law connects the pressure, volume, and absolute temperature of the same gas sample in two different states. When the amount of gas remains constant, you can use the relationship to solve for an unknown value.
P₁V₁ / T₁ = P₂V₂ / T₂
Assumptions and conditions
- The amount of gas remains constant.
- Temperature values must be absolute temperatures in Kelvin.
- Pressure values must be absolute pressure, not gauge pressure.
- Use consistent pressure units and consistent volume units for both states.
Frequently asked questions
What does the combined gas law calculate?
It relates the initial and final pressure, volume, and absolute temperature of a fixed amount of gas.
Can I enter Celsius?
This calculator accepts Kelvin. Convert Celsius to Kelvin by adding 273.15 before entering the value.
When should I use the combined gas law?
Use it when the same amount of gas changes state and pressure, volume, or temperature changes.
What is the combined gas law formula?
The formula is P1 × V1 / T1 = P2 × V2 / T2, where pressure is absolute pressure and temperature is in Kelvin.
Can I mix pressure or volume units?
Use consistent units for the initial and final states. If the units differ, convert them before calculating.
How to use this calculator
- Enter the known initial pressure, volume, and temperature.
- Enter the known final-state values requested by the calculator.
- Make sure temperatures are in Kelvin and pressure units are consistent.
- Select Calculate result to see the answer and working.
Important conditions
This relationship assumes a fixed amount of gas. Use absolute pressure rather than gauge pressure, and do not enter Celsius directly as a Kelvin value. For real gases at high pressure or near condensation, the idealized gas-law relationship may be less accurate.