Dew Point Calculator
Free online Dew Point Calculator that runs directly in your browser.
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Dew Point Calculator
Magnus-Tetens: e_s(T)=6.112·exp(a·T/(b+T)). Td = b·γ/(a−γ), γ=ln(RH/100)+a·T/(b+T). For ice a=22.46, b=272.62; for water a=17.62, b=243.12.
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Other tools you may find usefulDew point calculator - air temperature and humidity
This tool calculatesdew point (Td), frost temperature (Tf), water vapor pressureandabsolute humidity. Just enter the temperatureT_in, relative humidityRHand pressurep_in. The calculator uses the empirical Magnus-Tetens formulas and the Clausius–Clapeyron equation
Input data
- Air temperature T_in[°C or K]
- Relative humidity RH[%]
- Pressure p_in[Pa, hPa, kPa, bar, atm]
- Precision– number of decimal places (0–6)
Data can be entered in various units, the calculator automatically converts them to the SI system. For the standard atmosphere,p = 1013.25 hPa.
Formulas and calculation rules
1. Magnus formula for saturated vapor pressure
e_s = 6.112 · exp[(17.62 · T) / (243.12 + T)]
whereTis the temperature in °C,e_sin hPa.
2. Real vapor pressure
e = e_s · RH / 100
3. Dew point temperature
T_d = (243.12 · ln(e / 6.112)) / (17.62 − ln(e / 6.112))
4. Frosting temperature (Tf)
T_f = (272.62 · ln(e / 6.112)) / (22.46 − ln(e / 6.112))
5. Absolute and mixing humidity
AH = (216.7 e) / (T + 273.15) [g/m³] w = 621.97 · e / (p − e) [g/kg]
Units and conversions
| Quantity | Symbol | Unit |
|---|---|---|
| Temperature | T_in | °C / K |
| Relative humidity | RH | % |
| Pressure | p_in | Pa / hPa / kPa / bar / atm |
| Dew point | Td_C | °C |
| Temperature frost | Tf_C | °C |
| Absolute humidity | AH_gm3 | g/m³ |
| Mixing humidity | w_gpkg | g/kg |
Calculation examples
Example 1 - typical internal conditions
- T = 22°C
- RH = 50%
- p = 1013.25 hPa
e_s = 26.4 hPa, e = 13.2 hPa Td= 11.1°C, AH = 10.7 g/m³, w = 7.9 g/kg. The dew point is approximately 11°C, which means that condensation will start when the surface falls below this value.
Example 2 - cool and humid air
- T = 10°C
- RH = 90%
Td= 8.3°C, which explains the occurrence of dew in the morning, when the temperature drops below 9°C.
Practical applications
- Control of condensation on windows, pipes and HVAC devices
- Design of ventilation and dehumidification systems
- Microclimate analysis in greenhouses and laboratories
- Assessment of thermal comfort and internal conditions
FAQ
What is it dew point?
This is the temperature at which water vapor in the air begins to condense into water droplets.
Why does dew point depend on pressure?
At higher pressure, air can hold more water vapor, so the dew point increases with pressure.
How to lower the dew point in a room?
Reduce the relative humidity by ventilation or a dehumidifier, or lower the temperature of the condensation surface.
What is the difference between dew point temperature and frost point temperature?
The dew point refers to the condensation of water in the liquid state, and the frost point refers to the condensation of water in the solid state (frozen water vapor).
Summary
The dew point calculator uses the proven Magnus-Tetens model to calculate the temperature at which the air reaches saturation with water vapor. It allows you to quickly determine the risk of condensation, frost or excessive humidity. An ideal tool for analyzing climatic conditions in meteorology, construction and environmental engineering.