1. DPT & Relative Humidity Charts
Handy Dandy Earth Science Reference Tables Page 12

2. The “Dry Bulb” Don’t let it fool you. It is just a thermometer.
It measures the air temperature.
Duh!
20°C

3. The “Wet Bulb” Has a little wet booty tied to the bottom.
Gets cool when water evaporates.
12°C
Wet Booty

4. A Dry Day… A lot of moisture will evaporate.
The wet bulb will be a lot cooler than the dry bulb.
20°C
20°C
14°C
12°C
8°C
Difference between wet bulb & dry bulb is 12 °C.

5. A Humid Day… A little bit of moisture will evaporate.
The wet bulb will not be much cooler than the dry bulb.
20°C
14°C
Difference between wet bulb & dry bulb is 6 °C.

6. Page 12 of your Handy Dandy Earth Science Reference Tables
Warning #1: Be sure to READ the correct chart: DPT or RH
Warning #2: Dew Point Temperature IS NOT “Difference between wet bulb and dry bulb”.
Warning #3: The wet bulb temp IS NOT the DPT.

7. Dry-bulb temperature is your air temperature.
20 °C

8. 14 °C

9. 4 °C

10. Subtract (the difference) between the dry bulb and wet bulb

11. 20°C
14°C
20-14=6

12. 18°C
16°C
18-16=2

13. Put it all together
20°C
8°C
20-8=12
Relative Humidity = 11%

14. 14°C
10°C
14-10=4
Relative Humidity = 60%

15. The Dew Point Chart works the same way
14-10=4
Dew Point = 6°C

16. Try These. 57% 17 °C 86% 4 °C 57% 4 °C 91% 16 °C 100% 14 °C 45% -9 °C
Dry Bulb
Wet Bulb
R Humidity
DPT
26°C
20 °C
6 °C
5 °C
12 °C
8 °C
18 °C
17 °C
14 °C
0 °C
-3 °C
57%
17 °C
86%
4 °C
57%
4 °C
91%
16 °C
100%
14 °C
45%
-9 °C

17. More Difficult. 82% 18 °C 45.5% -.5 °C 100% 17 °C 20% -17 °C 69%
Dry Bulb
Wet Bulb
R Humidity
DPT
21°C
19°C
11°C
6 °C
17 °C
17°C
2°C
-3 °C
9°C
6.5 °C
70°F
60 °F
82%
18 °C
45.5%
-.5 °C
100%
17 °C
20%
-17 °C
69%
3.5 °C
15 °C
21 °C
52%
11 °C(50 °F)

19. The End