How to Calculate Actual Vapor Pressure

Actual Vapor Pressure Formula:

\[ e = \frac{RH}{100} \times e_s \]

Actual Vapor Pressure (e):

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1. What is Actual Vapor Pressure?

Definition: Actual vapor pressure (e) is the partial pressure of water vapor in the air, calculated from relative humidity and saturation vapor pressure.

Purpose: It's used in meteorology, HVAC design, and environmental studies to quantify atmospheric moisture content.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ e = \frac{RH}{100} \times e_s \]

Where:

\( e \) — Actual vapor pressure (Pa)
\( RH \) — Relative humidity (%)
\( e_s \) — Saturation vapor pressure (Pa)

Explanation: The formula converts relative humidity (a percentage) into actual vapor pressure by scaling the saturation vapor pressure.

3. Importance of Vapor Pressure Calculation

Details: Accurate vapor pressure measurements are critical for weather forecasting, building design, industrial processes, and understanding evaporation rates.

4. Using the Calculator

Tips: Enter relative humidity (0-100%) and saturation vapor pressure (must be > 0). The saturation vapor pressure can be calculated from temperature using the Clausius-Clapeyron equation.

5. Frequently Asked Questions (FAQ)

Q1: What units are used for vapor pressure?
A: Pascals (Pa) are standard, but other units like mmHg or hPa may be used with appropriate conversions.

Q2: How do I find saturation vapor pressure?
A: Use our Saturation Vapor Pressure Calculator or the Magnus formula based on temperature.

Q3: Why is actual vapor pressure important?
A: It directly affects evaporation rates, human comfort, and condensation potential.

Q4: What's typical range for actual vapor pressure?
A: In normal conditions, it ranges from about 600 Pa (cold/dry) to 3000 Pa (hot/humid).

Q5: How does altitude affect vapor pressure?
A: While the formula remains the same, saturation vapor pressure decreases with altitude due to lower air pressure.