Free · Gas laws
Gas Volume & Amount at Constant Temperature and Pressure
Use Avogadro’s relation to calculate one gas volume or amount from the other three positive values.
- Formula & worked example
- Private in your browser
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Calculator inputs
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How to use this calculator
- Enter the known values in the units shown. Results update as you type.
- Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
- Use the worked example to check the method. Reset restores the starting fields.
Private by default
Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.
Formula and method
At the same temperature and pressure, increasing gas amount from 2 mol to 3 mol changes a 4 m³ ideal-gas volume to 6 m³.
Initial volume ÷ initial amount = final volume ÷ final amount
Worked example
Enter these known values and leave the other values blank.
- Initial gas amount
- 2 mol
- Initial volume
- 4 m³
- Final gas amount
- 3 mol
- Final volume
- 6 m³
Assumptions and limitations
- Both states have the same temperature and pressure, and the ideal-gas approximation is appropriate.
- Gas amounts and volumes are positive. This model does not include a vacuum state, condensation or chemical reaction effects.
- The proportionality compares amount of substance, not mass unless molar mass is unchanged.
Common questions
Must temperature and pressure stay fixed?
Yes. If either changes, use a gas-law relation that includes those changes.
Can I use different volume units for each state?
Yes. Each retained selector converts its value into a common base before applying the relation.
References
- OpenStax: Gas Volume & Amount at Constant Temperature and Pressure
- NIST: exact mass, length and volume units
- Calculation definition and unit reference
Bookify requires positive gas amounts and volumes for the constant-temperature, constant-pressure ratio model.