Relative Humidity Calculator


About Relative Humidity Calculator (Formula)

Relative humidity (RH) is a crucial meteorological parameter that describes the amount of moisture in the air compared to the maximum amount the air can hold at a given temperature. It plays a significant role in weather forecasting, agriculture, HVAC (Heating, Ventilation, and Air Conditioning) systems, and various industries. Relative humidity can be calculated using the following formula:

Relative Humidity (RH) = (Actual Vapor Pressure / Saturation Vapor Pressure) x 100%


  • Relative Humidity (RH) is expressed as a percentage.
  • Actual Vapor Pressure is the pressure exerted by water vapor in the air, typically measured in millibars (mb), pascals (Pa), or inches of mercury (inHg).
  • Saturation Vapor Pressure is the maximum vapor pressure that the air can hold at a given temperature. It is also measured in millibars (mb), pascals (Pa), or inches of mercury (inHg).

To use this formula, you need to measure either the actual vapor pressure or both the temperature and the dew point temperature, from which you can calculate the actual vapor pressure. The saturation vapor pressure can be determined from temperature using established relationships or tables.

Why Relative Humidity Matters

Relative humidity is essential for several reasons:

  1. Weather Forecasting: Meteorologists use relative humidity to predict weather conditions, such as the likelihood of precipitation, fog, or thunderstorms. High relative humidity indicates a greater potential for rain, while low relative humidity can lead to dry and sunny conditions.
  2. Agriculture: Farmers monitor relative humidity to assess the risk of crop diseases, irrigation needs, and the comfort of livestock. High humidity can promote the growth of fungi and pests, while low humidity can cause dehydration in plants.
  3. HVAC Systems: In HVAC systems, maintaining appropriate relative humidity levels is essential for indoor comfort and health. Low humidity can lead to dry skin and respiratory issues, while high humidity can promote mold growth.
  4. Industrial Processes: Industries such as food production, pharmaceuticals, and electronics manufacturing depend on controlled humidity levels to ensure product quality and safety.

Using a Relative Humidity Calculator

A Relative Humidity Calculator simplifies the process of determining RH by automating the formula. Users input the necessary values, such as actual vapor pressure and saturation vapor pressure, and the calculator provides the RH percentage. Additionally, some calculators may allow users to input temperature and dew point to calculate RH directly.

In summary, relative humidity is a critical parameter that influences various aspects of our daily lives. Understanding and calculating relative humidity is essential for making informed decisions in fields ranging from weather forecasting to agriculture and indoor comfort control. A Relative Humidity Calculator streamlines the calculation process, making it accessible to a wide range of professionals and enthusiasts.