A JavaScript routine that calculates the relative humidity given the wet and dry bulb temperatures.
Enter the dry bulb temperature ( Tdry ) and wet bulb temperature ( Twet) in degrees Celsius, then click on the Calculate RH button
Tdry
Twet
How the calculation works:
1. The pressure is assumed to be 101.3 kPa (kiloPascals). 2. A conversion factor is calculated: A = 0.00066 (1.0 + 0.00115 Twb) 3. The saturation vapor pressure is calculated at Twb: eswb = e[(16.78 Twb - 116.9)/(Twb + 237.3)] 4. The water vapor pressure is calculated: ed = eswb - A P (Tdb - Twb) 5. The saturation vapor pressure is calculated at Tdb: esdb = e[(16.78 Tdb - 116.9)/(Tdb + 237.3)] 6. The relative humidity is then calculated: RH = 100 ed/esdb
1. The pressure is assumed to be 101.3 kPa (kiloPascals).
2. A conversion factor is calculated: A = 0.00066 (1.0 + 0.00115 Twb)
3. The saturation vapor pressure is calculated at Twb: eswb = e[(16.78 Twb - 116.9)/(Twb + 237.3)]
4. The water vapor pressure is calculated: ed = eswb - A P (Tdb - Twb)
5. The saturation vapor pressure is calculated at Tdb: esdb = e[(16.78 Tdb - 116.9)/(Tdb + 237.3)]
6. The relative humidity is then calculated: RH = 100 ed/esdb
This algorithm has been lifted from a U.S. Water Conservation Laboratory page which no longer exists.
Here's another version.
Debut: December 24, 1997. Revision 4. November 12, 2006. Index of other pages. Please send comments to Jeffrey Clymer. Visitors: