Van der Waals Equation Calculator.

Calculate pressure using the van der Waals equation with explicit SI gas constants.

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Set your values

Results update as you type.

02 / ANSWER

Amount of gas

Volume

Temperature

Attraction parameter a

Excluded-volume parameter b

Pressure

0.000000Pa

Results update automatically as you type.

Use Cases

Estimate real gas pressure in laboratory conditions

Use this calculator to find the pressure of a gas when you know its amount, volume, temperature, and the specific van der Waals constants for that gas. It helps in experimental setup and verification.

Example: Calculate the pressure of 2 mol of CO2 in a 0.01 m³ container at 300 K using a=0.3640 Pa·m⁶/mol² and b=4.267e-5 m³/mol.

Frequently Asked Questions

What does the van der Waals equation calculator do?: It computes the pressure of a real gas using the van der Waals equation: P = (nRT)/(V - nb) - a(n/V)^2. You input the amount of gas (mol), volume (m³), temperature (K), and the gas-specific constants a (Pa·m⁶/mol²) and b (m³/mol).
What are the units for the inputs?: All inputs must be in SI units: amount of gas in moles (mol), volume in cubic meters (m³), temperature in kelvin (K), attraction parameter a in Pa·m⁶/mol², and excluded-volume parameter b in m³/mol. The output pressure is in pascals (Pa).
Why does the van der Waals equation differ from the ideal gas law?: The van der Waals equation accounts for intermolecular attractions (parameter a) and the finite volume of gas molecules (parameter b). This makes it more accurate for real gases, especially at high pressures or low temperatures, where ideal gas assumptions break down.

Tips & Common Mistakes

Tips

Ensure all inputs are in SI units: moles, cubic meters, kelvin, Pa·m⁶/mol², and m³/mol. Convert if necessary.
Use the correct van der Waals constants for your specific gas. These are available in standard reference tables.
Check that the volume is greater than nb (the excluded volume). If V ≤ nb, the equation becomes invalid because the gas would be compressed beyond its molecular volume.
For high temperatures and low pressures, the van der Waals result approaches the ideal gas law, so you can use this calculator to see the difference.

Common Mistakes to Avoid

Using non-SI units like liters or atmospheres without converting. Always convert to m³ and Pa.
Forgetting to use the gas constant R in the correct units (8.314 J/(mol·K)) which matches the SI units of the other inputs.
Entering the temperature in Celsius instead of Kelvin. Add 273.15 to convert.

Last updated: August 13, 2026

Use Cases

Estimate real gas pressure in laboratory conditions

Example: Calculate the pressure of 2 mol of CO2 in a 0.01 m³ container at 300 K using a=0.3640 Pa·m⁶/mol² and b=4.267e-5 m³/mol.

Frequently Asked Questions

What does the van der Waals equation calculator do?

It computes the pressure of a real gas using the van der Waals equation: P = (nRT)/(V - nb) - a(n/V)^2. You input the amount of gas (mol), volume (m³), temperature (K), and the gas-specific constants a (Pa·m⁶/mol²) and b (m³/mol).

What are the units for the inputs?

All inputs must be in SI units: amount of gas in moles (mol), volume in cubic meters (m³), temperature in kelvin (K), attraction parameter a in Pa·m⁶/mol², and excluded-volume parameter b in m³/mol. The output pressure is in pascals (Pa).

Why does the van der Waals equation differ from the ideal gas law?

The van der Waals equation accounts for intermolecular attractions (parameter a) and the finite volume of gas molecules (parameter b). This makes it more accurate for real gases, especially at high pressures or low temperatures, where ideal gas assumptions break down.

Tips & Common Mistakes

Tips

Ensure all inputs are in SI units: moles, cubic meters, kelvin, Pa·m⁶/mol², and m³/mol. Convert if necessary.
Use the correct van der Waals constants for your specific gas. These are available in standard reference tables.
Check that the volume is greater than nb (the excluded volume). If V ≤ nb, the equation becomes invalid because the gas would be compressed beyond its molecular volume.
For high temperatures and low pressures, the van der Waals result approaches the ideal gas law, so you can use this calculator to see the difference.

Common Mistakes to Avoid

Using non-SI units like liters or atmospheres without converting. Always convert to m³ and Pa.
Forgetting to use the gas constant R in the correct units (8.314 J/(mol·K)) which matches the SI units of the other inputs.
Entering the temperature in Celsius instead of Kelvin. Add 273.15 to convert.

Use Cases

Estimate real gas pressure in laboratory conditions

Example: Calculate the pressure of 2 mol of CO2 in a 0.01 m³ container at 300 K using a=0.3640 Pa·m⁶/mol² and b=4.267e-5 m³/mol.

Frequently Asked Questions

What does the van der Waals equation calculator do?

What are the units for the inputs?

Why does the van der Waals equation differ from the ideal gas law?

Tips & Common Mistakes

Tips

Ensure all inputs are in SI units: moles, cubic meters, kelvin, Pa·m⁶/mol², and m³/mol. Convert if necessary.
Use the correct van der Waals constants for your specific gas. These are available in standard reference tables.
Check that the volume is greater than nb (the excluded volume). If V ≤ nb, the equation becomes invalid because the gas would be compressed beyond its molecular volume.
For high temperatures and low pressures, the van der Waals result approaches the ideal gas law, so you can use this calculator to see the difference.

Common Mistakes to Avoid

Using non-SI units like liters or atmospheres without converting. Always convert to m³ and Pa.
Forgetting to use the gas constant R in the correct units (8.314 J/(mol·K)) which matches the SI units of the other inputs.
Entering the temperature in Celsius instead of Kelvin. Add 273.15 to convert.