Vapor Pressure Calculator

The Vapor Pressure Calculator determines the vapor pressure of water at different temperatures using established thermodynamic relationships. This tool is essential for HVAC design, meteorology, and chemical engineering applications.

Modify the values and click the calculate button to use
Temperature °C
Temperature Unit  
Calculation Method
Pressure Units

Related Relative Humidity Calculator | Dew Point Calculator | Psychrometric Calculator

Understanding Vapor Pressure

Vapor pressure is the pressure exerted by water vapor in equilibrium with liquid water at a given temperature. It represents the tendency of water molecules to escape from the liquid phase into the vapor phase.

Key Concepts

Physical Meaning

Relationship to Other Properties

Calculation Methods

Magnus Formula (Recommended)

Formula: e = 6.112 × exp[(17.67 × T) / (T + 243.5)]

Range: -45°C to +60°C

Accuracy: ±0.1% over normal range

Units: e in kPa, T in °C

Antoine Equation

Formula: log₁₀(P) = A - B/(C + T)

Constants for Water: A = 8.07131, B = 1730.63, C = 233.426

Range: 1°C to 100°C

Accuracy: Very high for specified range

Goff-Gratch Equation

Application: Meteorological standard

Range: -100°C to +100°C

Accuracy: Highest precision available

Complexity: Most complex but most accurate

Applications

HVAC and Building Systems

Industrial Processes

Meteorology and Climate

Temperature Effects

Exponential Relationship

Vapor pressure increases exponentially with temperature:

Practical Implications

Unit Conversions

From To Multiply by
kPa Pa 1000
kPa mmHg 7.50062
kPa inHg 0.295300
kPa psi 0.145038

Accuracy Considerations

Method Selection

Error Sources

Practical Applications

Design Calculations

Process Control

Note: Vapor pressure calculations assume pure water. Real-world conditions may include dissolved substances that affect vapor pressure. For critical applications, consider these factors and use appropriate correction methods.