# DPT & Relative Humidity Charts

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

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

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

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.

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.

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.

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

14 °C

4 °C

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

20°C 14°C 20-14=6

18°C 16°C 18-16=2

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

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

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

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

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)

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