What is the Antoine equation?

The Antoine equation is a semi-empirical correlation relating vapor pressure to temperature: log₁₀(P) = A − B/(C+T). Constants A, B, and C are substance-specific and valid over a defined temperature range. It was proposed by Charles Marie Antoine in 1888.

What temperature units does the Antoine equation use?

Most tabulated Antoine constants (including the NIST WebBook values used here) use °C for temperature and mmHg for pressure. Some sources use Kelvin and kPa — always match your constants to the correct unit system.

Why does my result show "out of range"?

Antoine constants are only accurate within the temperature range they were fitted to. Extrapolating outside this range can give large errors. Use the valid range shown next to each preset substance.

How do I convert mmHg to other units?

The calculator converts automatically: 1 mmHg = 0.133322 kPa = 0.00131579 atm = 0.00133322 bar. All four values are displayed simultaneously.

Where do the preset Antoine constants come from?

The constants are sourced from the NIST WebBook and standard physical chemistry references (Perry's Chemical Engineers' Handbook). They represent the most widely cited values for each substance.

Can I use this for mixtures?

No — the Antoine equation applies to pure components only. For mixtures use Raoult's law combined with individual component vapor pressures calculated here.

Vapor Pressure Calculator

Calculate vapor pressure at any temperature using the Antoine equation with built-in constants for water, ethanol, methanol, benzene, and more.

Antoine Equation Inputs

Substance

Valid range: 1–100 °C

Temperature

Results

Enter a temperature and click Calculate

Vapor Pressure vs. Temperature

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Summary

The vapor pressure calculator uses the Antoine equation — log₁₀(P) = A − B/(C+T) — to compute the equilibrium vapor pressure of a pure liquid at a specified temperature. Select a preset substance to auto-fill the Antoine constants, or enter your own A, B, C values and temperature range. Results are returned in mmHg, kPa, bar, and atm simultaneously.

How it works

Select a preset substance (e.g., water, ethanol) or choose "Custom" to enter your own Antoine constants.
Enter the temperature in °C (or switch to Kelvin).
The calculator applies log₁₀(P) = A − B/(C+T) and displays vapor pressure in four unit systems.
A visual chart shows how vapor pressure changes across the valid temperature range for the selected substance.
Copy any result with one click.

Use cases

Determine boiling point elevation at various pressures in chemical engineering design.
Estimate evaporation rates of solvents in pharmaceutical and coating processes.
Verify thermodynamic data for distillation column simulations.
Teach and demonstrate the Antoine equation in physical chemistry courses.
Screen solvent volatility for safety assessments in industrial settings.
Cross-check experimental vapor pressure measurements against tabulated Antoine constants.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu