Vapor Pressure of Water Calculator
Calculate water vapor pressure using Antoine, Buck, Magnus, Tetens, and simple formulas
Calculate Water Vapor Pressure
Temperature at which to calculate vapor pressure
Most accurate overall • All temperatures
Vapor Pressure Results
Formula used: Buck Formula - Arden Buck equation
Temperature: 25.0°C (25°C)
All units: 3169 Pa • 0.0317 bar • 0.4595 psi
Temperature Analysis
All Formula Results Comparison
Buck Formula
Most accurate overall
Antoine Equation
Best for high temperatures
Magnus Formula
For meteorology
Tetens Formula
Best for 0-50°C
Simple Formula
General approximation
Example Calculation
Water at Room Temperature
Temperature: 25°C (77°F)
Expected vapor pressure: ~3.17 kPa
Buck formula result: P = 0.61121 × e^((18.678 - 25/234.5) × 25/(257.14 + 25))
Practical meaning: At room temperature, water has significant vapor pressure
Water at Boiling Point
Temperature: 100°C (212°F)
Expected vapor pressure: ~101.3 kPa (1 atm)
Significance: At 1 atmosphere pressure, water boils
Formula Accuracy Guide
Buck Formula
Most accurate overall
All temperature ranges
Antoine Equation
Best for high temperatures
0°C to 374°C
Tetens Formula
Best for 0-50°C range
Common temperatures
Pressure Unit Conversions
1 kPa = 1000 Pa
1 kPa = 7.501 mmHg
1 kPa = 0.00987 atm
1 kPa = 0.01 bar
1 kPa = 0.145 psi
Key Facts
Water boils when vapor pressure equals atmospheric pressure
Vapor pressure increases exponentially with temperature
Critical temperature for water is 374°C
At triple point (0.01°C), all three phases coexist
Understanding Vapor Pressure of Water
What is Vapor Pressure?
Vapor pressure is the pressure exerted by water vapor in thermodynamic equilibrium with liquid water in a closed system. It represents the tendency of water molecules to escape from the liquid phase and enter the gas phase.
Why is it Important?
- •Determines boiling point at different pressures
- •Critical for weather and humidity calculations
- •Essential in chemical engineering processes
- •Used in HVAC and refrigeration systems
Calculation Formulas
Buck Formula (Recommended)
P = 0.61121 × e^((18.678 - T/234.5) × T/(257.14 + T))
Most accurate for all temperatures
Antoine Equation
P = 10^(A - B/(C + T))
Semi-empirical, two parameter sets
Magnus/Tetens Formulas
P = C₁ × e^(C₂×T/(T + C₃))
Optimized for specific ranges
Practical Applications
Meteorology
Weather prediction, humidity calculations, and atmospheric modeling.
Engineering
HVAC design, distillation processes, and vacuum system design.
Chemistry
Phase diagrams, solution behavior, and reaction equilibria.