Relative Humidity

The Relative Humidity calculator computes the relative humidity based on the actual density of vapor and the saturated density.

INSTRUCTIONS: Choose units and enter the following:

• (W) Actual Density of Vapor
• (Ws) Saturation Density of Vapor

Relative Humidity(rh): The calculator returns the relative humidity as a percentage.

The Math / Science

Relative humidity is the amount of moisture in the air compared to what the air can "hold" at that temperature.  Relative Humidity is also a common index regarding human comfort maintaining a normal temperature.  Human comfort is ideally near 50% RH, while RD less than 30% is dry air and RD greater than 70% is considered humid.

When the air can't "hold" all the moisture,then it condenses as dew.

The formula for relative humidity is:

   rh = W/Ws

where:

• rh is the relative humidity converted to a percentage
• W is the actual density of the vapor
• Ws is the saturation density of the air.

Weather (Meteorology) Calculators

• Heat Index: Approximates the heat index based on the temperature and relative humidity
• Canadian Humidity Index (HUMIDEX): Computes the Canadian Humidity Index (HUMIDEX) based on the dry-bulb ambient temperature and the dew-point temperature.
• Australian Apparent Temperature (AT): Computes the apparent temperature based on the dry ambient temperature, the relative humidity and the wind speed at ten meters.
• Relative Humidity: Computes the relative humidity based on the actual density of vapor and the saturated density.
• Dew Point from Relative Humidity: Computes the dew point based on the relative humidity and ambient temperature.
• Summer Simmer Index: Computes the Summer Simmer Index based on the air temperature and relative humidity.
• Wind Chill Index (North America): Computes the wind chill index based on the air temperature and the velocity of the wind.
• Wet-Bulb Globe Temperature (WBGT): Computes the wet-bulb globe temperature index based on dry-bulb (air) temperature, globe thermometer temperature and the wet-bulb temperature.
• Humature Index: Estimates the humidity index based on the temperature and dew point.
• Antoine Equation: Computes the apparent vapor pressure of pure substances based on temperature and coefficients for the substance.
• Barometric Formula (Tropospheric) calculator computes the normal barometric pressure based on the altitude (h) using the Exponential Atmosphere formula.
• Planetary Temperature: Estimates a planet's temperature based on the luminosity of its star, distance to the star, average albedo and infrared optical depth of atmosphere.
• Snow Water Equivalent (SWE): Computes the volume of liquid water contained in rain or snow pack defined by area, depth and snow type or rain.

References

• http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/watvap.html