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Holsoft's Physics Resources Pages

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:
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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:
some space. Gerry Kuhn Environmental & Hygiene Engineering - Dust monitoring equipment. Legislation. Dust fallout. Dust watch. Dust monitoring. Dust particles. Occupational health and safety.  Hygiene engineering. Environmental engineeringequ: relative humidity. Gerry Kuhn Environmental & Hygiene Engineering - Dust monitoring equipment. Legislation. Dust fallout. Dust watch. Dust monitoring. Dust particles. Occupational health and safety.  Hygiene engineering. Environmental engineering
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):
some space. Gerry Kuhn Environmental & Hygiene Engineering - Dust monitoring equipment. Legislation. Dust fallout. Dust watch. Dust monitoring. Dust particles. Occupational health and safety.  Hygiene engineering. Environmental engineeringequ: partial vapour pressure. Gerry Kuhn Environmental & Hygiene Engineering - Dust monitoring equipment. Legislation. Dust fallout. Dust watch. Dust monitoring. Dust particles. Occupational health and safety.  Hygiene engineering. Environmental engineering
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:
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For a wider temperature range (T=0-50oC, error <0.1 kg/m3) use instead:
some space. Gerry Kuhn Environmental & Hygiene Engineering - Dust monitoring equipment. Legislation. Dust fallout. Dust watch. Dust monitoring. Dust particles. Occupational health and safety.  Hygiene engineering. Environmental engineeringequ: density of water. Gerry Kuhn Environmental & Hygiene Engineering - Dust monitoring equipment. Legislation. Dust fallout. Dust watch. Dust monitoring. Dust particles. Occupational health and safety.  Hygiene engineering. Environmental engineering
Density rhow 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:
some space. Gerry Kuhn Environmental & Hygiene Engineering - Dust monitoring equipment. Legislation. Dust fallout. Dust watch. Dust monitoring. Dust particles. Occupational health and safety.  Hygiene engineering. Environmental engineeringequ: density of air. Gerry Kuhn Environmental & Hygiene Engineering - Dust monitoring equipment. Legislation. Dust fallout. Dust watch. Dust monitoring. Dust particles. Occupational health and safety.  Hygiene engineering. Environmental engineering
Temperature T in Celcius; barometric pressure B in [Pa]; partial vapour pressure pv in [Pa]; rhoa: 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:
some space. Gerry Kuhn Environmental & Hygiene Engineering - Dust monitoring equipment. Legislation. Dust fallout. Dust watch. Dust monitoring. Dust particles. Occupational health and safety.  Hygiene engineering. Environmental engineeringequ: diffcoef of water vapour in air. Gerry Kuhn Environmental & Hygiene Engineering - Dust monitoring equipment. Legislation. Dust fallout. Dust watch. Dust monitoring. Dust particles. Occupational health and safety.  Hygiene engineering. Environmental engineering
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:
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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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