Online Calculators

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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 0-80^oC.
[Source: Monteith and Unsworth, 1990; some parameters slightly adjusted ]

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 (T_d and T_w, respectively; Celcius scale), partial vapour pressure is calculated by (at ambient pressure 1 atm):

where p_sat,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)]

density of water       [top]
Empirical relation for T=0-30^oC, error <0.1 kg/m³:

For a wider temperature range (T=0-50^oC, error <0.1 kg/m³) use instead:

Density _w in [kg/m³].
(Note: at 3.98^oC water has its highest density).
[Source: polynomial fit on values from Weast, 1986; page F-10]

density of (humid) air       [top]
Empirical relation:

Temperature T in Celcius; barometric pressure B in [Pa]; partial vapour pressure p_v 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]

diffusion coefficient of water vapour in air       [top]
Empirical relation:

T: temperature, Celcius [C]; D_v: diffusion coefficient [m²/s].
Error: <0.1×10^-6 m²/s; validity range: 0-45^oC.
[Source: linear fit on values given by Gates, 1980 (Appendix 3)]

viscosity of air       [top]
Empirical relation:

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

Holsoft (c) 2001