Aim: How to Determine Dew Point and Relative
Humidity
I. Determining Dew Point and Relative
Humidity
A. Find out dry bulb (air) temperature
B. Find out wet bulb temperature (Always cooler
than dry bulb. If it is the same temperature you
will have 100% relative humidity and the air is
said to be saturated.
C. Subtract the wet bulb temperature from the dry
bulb temperature (wet bulb depression).
D. Turn to your Dew Point or Relative Humidity
Chart in your E.S.R.T.
1. Find your dry bulb temperature on the left
side of the table.
2. Find your wet bulb depression on the top
of the table.
3. Follow the dry bulb temperature row until you
hit the wet bulb depression column. This is your
Dew Point or Relative Humidity reading.
(Remember: Dew Point readings are in oC and
Relative Humidity readings are in %).
E. What to do if you have an odd dry bulb
temperature.
1. Find the even dry bulb values above and
below your odd temperature. Ex: If the dry
bulb reading is 9oC, look at 8oC and 10oC.
2. Find out the values for each of the even
temperatures.
3. Pick a value in between the even temperature
values.
Daily Relative Humidity Changes