<p>The <a href="http://www.engineeringtoolbox.com/specific-relative-humidity-air-d_688.html" rel="nofollow">Engineering Toolbox</a> gives the following equation for converting relative humidity to specific humidity.</p>

<blockquote>
  <p>If we know the relative humidity of the moist air and the water vapor density and density of the air, the specific humidity can be expressed as:</p>
</blockquote>

<pre><code>x = 0.622 φ ρws / (ρ - ρws) 100%         (1)

where

x = specific humidity of air vapor mixture (kg/kg)

φ = relative humidity (%)

ρws = density of water vapor (kg/m3)

ρ = density of the moist or humid air (kg/m3)
</code></pre>

CC BY-SA 3.0
2015-06-24T07:07:14.247Z
2015-06-24T07:07:14.247Z
Fred
<p>I am using NCEP_DOE reanalysis 2 data set. It include only relative humidity while I need specific humidity. How do I convert the relative humidity into specific humidity?</p>

CC BY-SA 3.0
2015-07-02T15:23:36.423Z
there is a nice answer to this here: http://earthscience.stackexchange.com/q/5076/174
David LeBauer
<meteorology><atmosphere-modelling>
How do I convert Relative Humidity into specific humidity
HASSAN
# How do I convert Relative Humidity into specific humidity

(Asked by: username_0 on 2015-06-24)

I am using NCEP\_DOE reanalysis 2 data set. It include only relative humidity while I need specific humidity. How do I convert the relative humidity into specific humidity?

**Tags:** meteorology, atmosphere-modelling

> **Comments:**
> **username_1**: there is a nice answer to this here: http://earthscience.stackexchange.com/q/5076/174  

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## 1 answers

### Answer by username_2 on 2015-06-24. Score: 3 | Accepted answer

The Engineering Toolbox gives the following equation for converting relative humidity to specific humidity.

If we know the relative humidity of the moist air and the water vapor density and density of the air, the specific humidity can be expressed as:

x = 0.622 φ ρws / (ρ - ρws) 100%         (1)

where

x = specific humidity of air vapor mixture (kg/kg)

φ = relative humidity (%)

ρws = density of water vapor (kg/m3)

ρ = density of the moist or humid air (kg/m3)


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