1. What is a Vapor Pressure of Water Calculator?

Definition: This calculator determines the vapor pressure of water at a given temperature using one of five formulas (Simplified, Antoine, Magnus, Tetens, or Buck), selected by the user, outputting results in multiple pressure units.

Purpose: It is used in chemistry and thermodynamics to predict the vapor pressure of water, aiding in humidity calculations, phase transition studies, and environmental science applications.

2. How Does the Calculator Work?

The calculator uses the selected formula for vapor pressure of water, outputting in all specified pressure units (Pa, bar, psi, at, atm, Torr, hPa, kPa, MPa, GPa, inHg, mmHg):

• 1. **Simplified Formula**: \( P_{\text{simple}} = (e^{20.386 - 5132/(T + 273.15)}) \times 0.1325 \) (kPa, \(T\) in K, adjusted for 3.157 kPa at 25°C)
• 2. **Antoine Formula**: \( P_{\text{Antoine}} = (10^{8.07131 - 1730.63/(233.426 + T)}) \times 0.1326 \) (kPa, \(T\) in °C, adjusted for 3.158 kPa at 25°C)
• 3. **Magnus Formula**: \( P_{\text{Magnus}} = 0.61094 \times e^{17.625 \times T/(T + 243.04)} \) (kPa, \(T\) in °C, matches 3.162 kPa at 25°C)
• 4. **Tetens Formula**: \( P_{\text{Tetens}} = 0.61078 \times e^{17.27 \times T/(T + 237.3)} \) (kPa, \(T\) in °C, matches 3.1677 kPa at 25°C)
• 5. **Buck Formula**: \( P_{\text{Buck}} = 0.61121 \times e^{(18.678 - T/234.5) \times T/(257.14 + T)} \) (kPa, \(T\) in °C, matches 3.1685 kPa at 25°C)

Explanation: Select a formula from the dropdown, then enter the water temperature (e.g., 25°C). The calculator converts the temperature to the required units (Celsius for most formulas, Kelvin for the Simplified formula), computes the vapor pressure using the selected formula, and outputs results in all specified pressure units.

Notes on Units: Ensure the temperature is positive and physically meaningful (e.g., above absolute zero). All formulas output in kPa as the base unit, then convert to Pa, bar, psi, at, atm, Torr, hPa, kPa, MPa, GPa, inHg, and mmHg.

3. Importance of Vapor Pressure of Water

Details: Vapor pressure of water is crucial for understanding humidity, evaporation rates, and phase transitions, impacting weather prediction, material processing, and environmental science.

4. Using the Calculator

Tips: Select a formula from the dropdown, then input the water temperature with its unit (Celsius, Fahrenheit, or Kelvin). Ensure the temperature is positive and within a reasonable range for water’s vapor pressure (typically 0°C to 100°C, but it can handle a broader range). Results are approximate and may vary slightly due to formula assumptions or non-ideal conditions.

Vapor Pressure of Water Calculator© - All Rights Reserved 2025