Vapor Pressure Calculator — Antoine Equation
Find the equilibrium vapor pressure of water, ethanol, acetone, benzene, and other common liquids at any temperature using the Antoine equation. Pre-loaded constants from Stull (1947) as tabulated in NIST WebBook; custom constants are also accepted.
Compound
°C
Saturation (vapor) pressure at the given temperature
- 1
Denominator C + T
233.426 + 25 = 258.426 - 2
Antoine log₁₀(P/mmHg)
8.07131 − 1,730.63 ÷ 258.426 = 1.374499 - 3
Vapor pressure (mmHg)
10^1.374499 = 23.6864 - 4
Vapor pressure (kPa)
23.6864 × 0.133322 = 3.1579Convert from mmHg to kPa (1 mmHg = 0.133322 kPa).
How does this calculator work?
log₁₀(P/mmHg) = A − B/(C + T°C) — that's the Antoine equation. Choose a compound (water, ethanol, acetone, benzene…) to auto-load its Stull/NIST constants, enter a temperature in °C, and get the equilibrium vapor pressure in Pa, kPa, bar, atm, and mmHg, plus a full pressure-vs-temperature curve.
Formula
How this is calculated
The Antoine equation is the standard empirical correlation for the temperature-dependence of vapor pressure. It has the form log₁₀(P) = A − B/(C + T), where P is the saturation pressure in mmHg and T is temperature in °C; A, B, and C are substance-specific constants fitted to experimental data. Raising temperature increases vapor pressure exponentially — a consequence of the Clausius-Clapeyron relation — which is why the Antoine equation uses a logarithmic scale.
The calculator converts the result from mmHg to SI units (Pa, kPa) and practical units (bar, atm) automatically. The plot shows the full curve over the valid temperature range for the selected compound, giving a visual sense of where the normal boiling point lies (vapor pressure = 101.325 kPa ≈ 1 atm).
The pre-loaded Antoine constants are from Stull (1947) as cited in Perry's Chemical Engineers' Handbook and the NIST WebBook. Each compound has a stated valid temperature range; extrapolation beyond this range is possible but adds increasing uncertainty. For custom compounds, enter your own A, B, C values from a reliable source, ensuring they match the same units (P in mmHg, T in °C).
Frequently asked questions
The original Antoine (1888) and most historical datasets use mmHg and °C — these constants are the most widely tabulated. The calculator converts automatically to Pa, kPa, bar, and atm so you can use whichever unit your application requires.
The normal boiling point is the temperature at which vapor pressure equals 1 atm (101,325 Pa = 760 mmHg). For water the Antoine equation predicts this correctly at about 100 °C. You can read it off the curve where the pressure line crosses 101.3 kPa.
Yes — select Custom and enter your own A, B, C. Just confirm the units match: this calculator assumes log₁₀(P/mmHg) = A − B/(C + T/°C). If your source uses natural log or different pressure/temperature units, convert the constants first.
Also known as
TG we-Calculate Editorial Team. (2026). Vapor Pressure Calculator — Antoine Equation [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/vapor-pressure-calculator
TG we-Calculate Editorial Team. "Vapor Pressure Calculator — Antoine Equation." TG we-Calculate. 2026. https://we-calculate.com/calculator/vapor-pressure-calculator.
TG we-Calculate Editorial Team, "Vapor Pressure Calculator — Antoine Equation," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/vapor-pressure-calculator
@misc{wecalculate_vapor_pressure_calculator, title = {Vapor Pressure Calculator — Antoine Equation}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/vapor-pressure-calculator}}, year = {2026}, note = {TG we-Calculate} }
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