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There are two main approaches to calculate dew point and relative humidity:
1. Using a psychrometer or hygrometer:
These instruments directly measure humidity and some models can also provide dew point readings.
2. Using mathematical formulas:
There are a couple of formulas you can use to calculate dew point and relative humidity if you know the air temperature and either the relative humidity or the dew point.
- Calculating dew point from temperature and relative humidity:
A relatively simple and accurate formula for dew point (Td) in degrees Celsius is:
Td = T – ((100 – RH)/5)
where:
- T is the air temperature in degrees Celsius
- RH is the relative humidity in percent
This formula is most accurate for higher relative humidity values (above 50%).
- Calculating relative humidity from temperature and dew point:
The equations to calculate relative humidity (RH) are more complex and involve exponential terms. Here’s one option:
RH = 100 * (EXP((17.625 * Td) / (243.04 + Td)) / EXP((17.625 * T) / (243.04 + T)))
where:
- Td is the dew point temperature in degrees Celsius
- T is the air temperature in degrees Celsius
- EXP is the mathematical exponent function (available on most calculators)
