Vapor Pressure Calculator
Convert temperature to vapor pressure using the Antoine correlation. Provide substance specific constants for accurate results.
Vapor pressure (mmHg)
23.686
Vapor pressure (kPa)
3.158
How to Use This Calculator
Collect Antoine constants
Look up A, B, and C constants for the substance over the applicable temperature range.
Enter temperature
Provide the liquid temperature in Celsius within the correlation range.
Apply the Antoine equation
The calculator computes log10(P) = A - B/(C + T) and converts to mmHg and kilopascals.
Interpret pressure
Use the resulting vapor pressure to compare with system pressure or for phase equilibrium calculations.
Formula
log10(P) = A - B / (C + T)
P is in mmHg when using standard Antoine constants. Convert to other units using P(kPa) = P(mmHg) * 0.133322368.
Example
For water at 25 C with constants above: log10(P) = 8.07131 - 1730.63/(233.426 + 25) = 1.336, so P = 21.7 mmHg (2.89 kPa).
Full Description
The Antoine equation provides an empirical fit between temperature and vapor pressure for many substances over limited ranges.
It is widely used in distillation, evaporation, and safety calculations where quick vapor pressure estimates are required without tabulated data.
Frequently Asked Questions
Where do I find Antoine constants?
Engineering handbooks, databases, and product datasheets list constants segmented by temperature ranges.
Can I input Kelvin?
Convert Kelvin to Celsius by subtracting 273.15 before entering the temperature.
What if my constants use bar?
Follow the equation units associated with the constants. Convert the final pressure to your preferred unit afterward.
Does this work for mixtures?
No. Antoine constants are for pure components. For mixtures, use activity coefficients or Raoult's law.
How accurate is the equation?
Accuracy depends on the temperature range and quality of constants. Deviations increase near critical or triple points.