Relative Humidity Calculator

What is Relative Humidity?

“Relative Humidity is a measure of the amount and moisture content at a specific temperature and dew point.” 

Being a user, you need to find the RH in Celcius, Farehhite, or Kelvin scale. The RH Calculator allows the users to know the RH at a specific temperature unit.

How to Calculate Relative Humidity (RH)?

The dew point (Td), air temperature (T), and relative humidity (RH) are related to each other.  These variables are related by the Magnus-Tetens formula. The relative humidity formula is:

\[Td = \frac{a \cdot (\ln(RH/100) + \frac{b \cdot T}{c + T})}{a - (\ln(RH/100) + \frac{b \cdot T}{c + T})}\]

Where:

• Td = Dew point 
•  T =  Air temperature 
• RH = Relative Humidity 
• a, b, c = constants

Example:

Let's suppose on a specific day the air temperature is 25°C and the dew point is 25°C. Then what is the Relative Humidity (RH)?

Given:

\(T = 25^\circ C\)

Dew point = 25°C

The constants for water are:

\(A = 611.21 \, \text{Pa}\)

\(B = 17.502\)

\(C = 240.97^\circ C\)

Solution:

The relative humidity equation is:

\[ e = 611.21 \cdot \exp\left(\frac{17.502 \cdot 25}{25 + 240.97}\right) \]

Calculate \(e\):

\[ e \approx 611.21 \cdot \exp\left(\frac{437.55}{265.97}\right) \approx 611.21 \cdot 1.647 \approx 1004.6 \, \text{Pa} \]

Calculate Saturation Vapor Pressure \(e_s\) at 25°C:

\[ e_s = 611.21 \cdot \exp\left(\frac{17.502 \cdot 25}{25 + 240.97}\right) \approx 1004.6 \, \text{Pa} \]

Relative Humidity:

\[ RH = \frac{e}{e_s} \times 100 = \frac{1004.6}{1004.6} \times 100 = 100\% \]

You can check the RH of the air at a specific temperature and pressure with our Relative Humidity Calculator for instant results.

Working of Relative Humidity Calculator:

The temperature and moisture content are the basic while calculating the RH by the relative humidity calculator.  Let's see how it works!

Input Parameters:

• Temperature 
•  Dew point

Ouput Result:

• Relative Humidity

FAQs:

What is Humidity Definition?

Humidity is the measure of the amount of water vapor in the air at a specific temperature and pressure and the phenomenon is called the Wet bulb effect. Humidity is directly proportional to the amount of water. In the weather forecast, the humidity is referred to as the relative humidity

What is 100% Relative Humidity?

If the relative humidity is 100 percent then the dewpoint temperature and actual air temperature are the same.

What is the Ideal Relative Humidity for Health?

The ideal relative humidity for health and comfort is somewhere between 30-50% humidity.

What Happens at 0% Humidity?

Given the Earth's climate and weather conditions, it is impossible to have zero humidity. Water vapor is always present in the air or a trace of water is there.

Citations:

From Weather.Gov: Relative Humidity, Water Vapour From ScienceDirect.Com: RH, Psychrometrics