Relative Humidity Converter

Category: Weather Converters
- February 10, 2025
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Dew point must be less than or equal to air temperature

Humidity Comfort Levels:

  • Too Dry: < 30% RH
  • Comfortable: 30-50% RH
  • Moderate: 50-60% RH
  • Humid: 60-70% RH
  • Very Humid: > 70% RH

Relative humidity (RH) is a crucial factor in weather, indoor comfort, and various industrial applications. Understanding how to calculate RH can help in assessing air quality, preventing mold growth, and improving HVAC efficiency.

What is Relative Humidity?

Relative humidity is the percentage of moisture in the air compared to the maximum amount the air can hold at a given temperature. It is expressed as:

$$ RH = \left( \frac{e(T_{dew})}{e(T_{air})} \right) \times 100\% $$

Where:

  • e(Tdew): Actual vapor pressure at the dew point
  • e(Tair): Saturation vapor pressure at air temperature

How to Calculate Relative Humidity

The Magnus formula is widely used for estimating vapor pressure:

$$ e(T) = 6.112 \times \exp \left( \frac{17.27 \times T}{237.7 + T} \right) $$

Using this, RH is calculated as:

$$ RH = \left( \frac{6.112 \times \exp \left( \frac{17.27 \times T_{dew}}{237.7 + T_{dew}} \right)}{6.112 \times \exp \left( \frac{17.27 \times T_{air}}{237.7 + T_{air}} \right)} \right) \times 100\% $$

Why is Relative Humidity Important?

Relative humidity impacts multiple aspects of daily life, including:

  • Comfort: Optimal RH for indoor air is between 30-50%.
  • Health: High humidity promotes mold and dust mites, while low RH can cause dryness and respiratory discomfort.
  • HVAC Efficiency: Maintaining proper RH reduces energy consumption in heating and cooling systems.
  • Material Preservation: Museums, libraries, and storage facilities use RH control to prevent material degradation.

How to Use the Relative Humidity Converter

The Relative Humidity Converter simplifies RH calculation by taking:

  1. Air Temperature in °C or °F
  2. Dew Point in °C or °F

After entering values, the tool computes RH and categorizes it into:

  • Too Dry: < 30%
  • Comfortable: 30-50%
  • Moderate: 50-60%
  • Humid: 60-70%
  • Very Humid: > 70%

Example Calculation

If the air temperature is 25°C and the dew point is 15°C:

$$ RH = \left( \frac{6.112 \times \exp \left( \frac{17.27 \times 15}{237.7 + 15} \right)}{6.112 \times \exp \left( \frac{17.27 \times 25}{237.7 + 25} \right)} \right) \times 100\% $$

Result: The relative humidity is approximately **50%**, which falls within the comfortable range.

Conclusion

Understanding relative humidity helps in maintaining indoor comfort, optimizing HVAC performance, and preserving sensitive materials. Use the Relative Humidity Converter for quick and accurate calculations.