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# Online Calculators

online calculators listed below:
saturated vapour pressure
relative humidity of air
density of water
density of (humid) air
diffusion coefficient of water vapour in air
viscosity of air

Note:
Temperatures on this page are on the Celcius scale. If you are more familiar with Fahrenheits, you may want to see what a value in Celcius would be in Fahrenheit: use our F/C Converter.

saturated vapour pressure (SVP)       [top]
Saturated water vapour pressure in air; empirical relation:  Temperature T in Celcius [ = {Kelvin} - 273.15]); validity range roughly 0-80oC.
[Source: Monteith and Unsworth, 1990; some parameters slightly adjusted ]

saturated vapour pressure
 Temperature [oC]: Sat. vapour pressure [Pa]:

relative humidity of air       [top]
Relative humidity is the ratio of partial vapour pressure and saturated vapour pressure at ambient temperature:  If humidity is to be determined by dry- and wet-bulb temperatures (Td and Tw, respectively; Celcius scale), partial vapour pressure is calculated by (at ambient pressure 1 atm):  where psat,w is saturated vapour pressure at the wet-bulb temperature. Finally, saturated vapour pressure at dry-bulb temperature (i.e. normal ambient temperature) must be calculated, and the pressure ratio gives relative humidity.
[Source: calculator for saturated vapour pressure (see above) and relation between bulb temperatures and vapour pressures (List, 1958)]
relative humidity
 Dry-bulb temperature [oC]: Wet-bulb temperature [oC]: Relative humidity [%]:

density of water       [top]
Empirical relation for T=0-30oC, error <0.1 kg/m3:  For a wider temperature range (T=0-50oC, error <0.1 kg/m3) use instead:  Density w in [kg/m3].
(Note: at 3.98oC water has its highest density).
[Source: polynomial fit on values from Weast, 1986; page F-10]
density of water (0-50oC)
 Temperature [oC]: Density of water [kg/m3]:

density of (humid) air       [top]
Empirical relation:  Temperature T in Kelvin [K]; barometric pressure B in [Pa]; partial vapour pressure pv in [Pa]; a: density [kg/m3]; validity range: 'environmental' values. (Note: 1 atm = 1.01325 x 105 Pa)
[Source: Weast, 1986; page F-8; modified for SI units]
density of air
 Temperature [oC]: Barometric pressure [Pa]: Relative humidity [%]: Density of air [kg/m3]:

diffusion coefficient of water vapour in air       [top]
Empirical relation:  T: temperature, Celcius [C]; Dv: diffusion coefficient [m2/s].
Error: <0.1x10-6 m2/s; validity range: 0-45oC.
[Source: linear fit on values given by Gates, 1980 (Appendix 3)]
diffusion coefficient of water vapour in air
 Temperature [oC]: Diffusion coefficient [10-6 m2/s]:

viscosity of air       [top]
Empirical relation:  T: temperature, Celcius [C]; viscosity in Pascal x seconds [Pa.s]>.
Error: <0.1x10-6 Pa.s; validity range: 0-54oC.
[Source: parabolic fit on values from Weast, 1986; page F-42]
viscosity of air
 Temperature [oC]: Viscosity [10-6 Pa.s]:

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