How Do You Calculate the Dew Point?
To calculate dew point, you need to know the current temperature and relative humidity, and then solve the equation Td = T – ((100 – RH) / 5) for Td, which stands for the dew point temperature in degrees Celsius. This equation is accurate for humidity values above 50 percent.

Learn the dew point equation
The simple equation for dew point is: Td = T – ((100 – RH) / 5). “Td” stands for the dew point temperature in degrees Celsius. “T” stands for the observed temperature in degrees Celsius. RH is the relative humidity in percent. Relative humidity is the ratio of how much moisture the air is holding to how much moisture it could hold at a given temperature.

Plug the values into the equation
Put the values for the temperature and relative humidity into the equation. For example, if the observed temperature is 19 degrees Celsius and the relative humidity is 75 percent, the equation reads: Td = 19 – ((100 – 75) / 5).

Solve the equation
Solve the equation to find the dew point temperature. To continue the example: Td = 19 – ((100 – 75) / 5) = 19 – (25 / 5) = 19 – 5 = 14. This result means that the dew point temperature is 14 degrees Celsius.