Antoine Equation Vapour Pressure Calculator
Vapour pressure of a liquid at a given temperature from its Antoine constants, in mmHg, kPa and bar.
Results
What this tool does
Vapour pressure rises steeply and non-linearly with temperature, and the Antoine equation is the three-constant fit that chemical engineering has used for over a century to describe it. Distillation columns, flash calculations, solvent exposure limits and the design of any vessel holding a volatile liquid all start here. The constants belong to one substance and one temperature window, so they must always be quoted with both.
Formula
log10(P) = A - B / (C + T)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
aa | Antoine constant A | — |
bb | Antoine constant B | — |
cc | Antoine constant C | — |
tt | Temperature | °C |
PM | Vapour pressure | mmHg |
PK | Vapour pressure | kPa |
PB | Vapour pressure | bar |
TB | Boiling point | °C |
Worked example
- Antoine constant A8.07131
- Antoine constant B1730.63
- Antoine constant C233.426
- Temperature25 °C
- Vapour pressure23.6864 mmHg
- Vapour pressure3.15793 kPa
- Vapour pressure0.031579 bar
- Boiling point100.00 °C
Limitations
- Coverage and consumption figures vary between products. Take the values from the manufacturer's datasheet for the product you are actually using.
- The default values are typical reference figures, not measurements of your situation. Replace them with your own data whenever you have it.
- Mixing units is the most common source of error. Convert every input to the units shown next to each field before calculating.
Frequently asked questions
Where do A, B and C come from?
They are fitted to measured vapour pressure data for one specific substance over one specific temperature range, and they are meaningless outside it. They also depend on the units: the same liquid has different constants for mmHg and for kPa, and for °C and for K. Always take the set from a source that states both the units and the valid range. The defaults here are water in mmHg and °C, valid from 1 to 100 °C.