<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](http://www.engineeringtoolbox.com/specific-relative-humidity-air-d_688.html) 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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