1. What is Relative Humidity?

Relative humidity (RH) is the ratio of the current amount of water vapor in the air to the maximum amount that could be present at that temperature, expressed as a percentage. It indicates how close the air is to being saturated with moisture.

2. How Does the Calculator Work?

The calculator uses the relative humidity formula:

Where:

• \( RH \) — Relative humidity (%)
• \( e(T_d) \) — Saturation vapor pressure at dewpoint temperature (kPa)
• \( e(T) \) — Saturation vapor pressure at air temperature (kPa)

The saturation vapor pressure is calculated using the Magnus formula: \[ e(T) = 0.6108 \times \exp\left(\frac{17.27 \times T}{T + 237.3}\right) \] where \( T \) is temperature in °C.

Explanation: The dewpoint temperature is the temperature to which air must be cooled to become saturated with water vapor. The ratio of vapor pressures at dewpoint and actual temperature gives the relative humidity.

3. Importance of Relative Humidity

Details: Relative humidity affects human comfort, building design, industrial processes, and weather forecasting. It's crucial for understanding apparent temperature, mold growth potential, and material preservation.

4. Using the Calculator

Tips: Enter both the current air temperature and dewpoint temperature in °C. The dewpoint must always be equal to or lower than the air temperature for valid results.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between dewpoint and relative humidity?
A: Dewpoint is an absolute measure of moisture in the air (temperature at which condensation forms), while RH is a relative measure that depends on both moisture content and air temperature.

Q2: What are typical comfortable RH levels?
A: For human comfort, 30-50% RH is generally recommended. Below 30% may feel dry, above 60% feels humid and can promote mold growth.

Q3: Why does RH change throughout the day?
A: RH varies inversely with temperature when moisture content is constant - highest at night when coolest, lowest in afternoon when warmest.

Q4: What's the relationship between RH and dewpoint?
A: When air temperature equals dewpoint, RH is 100% (saturation). The greater the difference between temperature and dewpoint, the lower the RH.

Q5: Are there limitations to this calculation?
A: The Magnus formula approximation works well for typical atmospheric conditions but may have slight errors at extreme temperatures or pressures.