Chemistry

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Vapor Pressure Calculator.

Evaluate the Antoine vapor-pressure equation with user-supplied coefficients and units.

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How to Use

log₁₀(P) = A − B/(C + T). Enter coefficients from a named Antoine correlation and its native pressure-to-kPa scale.

Use a named source convention for coefficients and units. This page does not provide laboratory, medical, species, or food-safety advice.

Use Cases

Chemical Engineering Process Design

Estimate vapor pressure for distillation, evaporation, or condensation processes to design equipment and set operating conditions.

Example: Calculate vapor pressure of water at 80°C using Antoine coefficients to size a condenser.

Laboratory and Research Applications

Quickly compute vapor pressure for pure substances in experiments, calibration, or when preparing solutions.

Example: Determine vapor pressure of ethanol at 25°C for a gas chromatography experiment.

Frequently Asked Questions

What is the Antoine equation?
The Antoine equation is a semi-empirical formula that relates vapor pressure to temperature. It uses three substance-specific coefficients (A, B, C) and is commonly used in chemistry and engineering to estimate vapor pressure over a limited temperature range.
How do I use this calculator?
Enter the Antoine coefficients (A, B, C) for your substance, choose the temperature unit (e.g., Celsius, Fahrenheit, Kelvin), and input the temperature. The calculator will compute the vapor pressure using the Antoine equation and display the result in your selected pressure unit.
What units can I use?
The calculator allows you to select temperature units (Celsius, Fahrenheit, Kelvin) and pressure units (e.g., atm, mmHg, kPa, bar). Ensure your Antoine coefficients are consistent with the chosen temperature unit, as the equation is unit-sensitive.

Tips & Common Mistakes

Tips

  • Ensure your Antoine coefficients (A, B, C) are for the same temperature unit you select (e.g., if coefficients are for °C, choose Celsius).
  • The Antoine equation is valid only over a specific temperature range; check that your temperature is within the range for which the coefficients were derived.
  • Double-check the pressure unit you want; the calculator will output in the unit you select, but coefficients may be based on a specific pressure unit (e.g., mmHg).
  • For mixtures or non-ideal systems, the Antoine equation may not be accurate; consider using more advanced models.

Common Mistakes to Avoid

  • Using coefficients that are not compatible with the selected temperature unit (e.g., using °C coefficients with Kelvin temperature).
  • Forgetting to convert temperature to the correct scale if the coefficients require a different unit.
  • Assuming the Antoine equation is valid for all temperatures; it is only accurate within a limited range.

Last updated: August 13, 2026