Vapor Pressure of Water Calculator

Find the saturation vapor pressure of water at a given temperature.

How the Math Works

The Vapor Pressure of Water Calculator uses the Tetens equation: P = 0.61078 * e^(17.27T/(T+237.3)), where P is the vapor pressure in kilopascals (kPa) and T is the temperature in Celsius. This formula models how water vapor pressure increases with temperature through an exponential relationship. The constants 0.61078, 17.27, and 237.3 are empirically derived to align with experimental data, ensuring accuracy across typical Earth temperatures. The exponent (17.27T/(T+237.3)) captures the non-linear behavior of vapor pressure, where small temperature changes significantly affect the result, especially at extreme values.

Practical Applications

To use this calculator, input the current air temperature in Celsius, and it outputs the saturation vapor pressure of water. This value is critical in meteorology for predicting weather patterns, such as determining dew point or relative humidity when combined with actual vapor pressure measurements. In agriculture, it helps optimize irrigation by estimating water loss through evaporation. Food scientists and chefs rely on it for processes like steam cooking or drying, where controlling humidity is essential. HVAC engineers also use it to design systems that maintain comfortable indoor humidity levels by adjusting heating, cooling, or humidification.

Day-to-Day Use

Understanding water vapor pressure impacts daily activities in subtle but meaningful ways. For instance, knowing the vapor pressure helps explain why clothes dry faster on humid days or why certain plants require more water in hot, dry climates. In the kitchen, it clarifies why boiling water at high altitudes takes longer—lower atmospheric pressure reduces the vapor pressure needed for boiling. Additionally, in home environments, maintaining optimal humidity levels (via vapor pressure calculations) prevents issues like mold growth, static electricity, or dry skin, enhancing comfort and health. These insights empower better decision-making in gardening, cooking, and climate control.

Worked example

25 °C → ~3.17 kPa (23.8 mmHg).

FAQ