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Dew point calculator

Invert the August-Roche-Magnus relative humidity equation to estimate dew point.

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Answer

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Invert the August-Roche-Magnus relative humidity equation to estimate dew point.

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Precision and calculation record
Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.
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Formula and assumptions
Uses coefficients 17.625 and 243.04 C from the EPA humidity algorithm. This implementation accepts air temperatures from 0 to 50 C and reports dew point over liquid water, including a subzero liquid-water dew point. It does not calculate frost point or replace a calibrated humidity instrument.
Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.
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Updated 
Using Dew point calculator
Invert the August-Roche-Magnus relative humidity equation to estimate dew point.
Uses coefficients 17.625 and 243.04 C from the EPA humidity algorithm. This implementation accepts air temperatures from 0 to 50 C and reports dew point over liquid water, including a subzero liquid-water dew point. It does not calculate frost point or replace a calibrated humidity instrument.
Next: Temperature converter
A worked example
For air temperature (degrees c) = 20, relative humidity (%) = 50, dew point (degrees c) = 9.261107.
Before you use the result
Uses coefficients 17.625 and 243.04 C from the EPA humidity algorithm. This implementation accepts air temperatures from 0 to 50 C and reports dew point over liquid water, including a subzero liquid-water dew point. It does not calculate frost point or replace a calibrated humidity instrument.
Example results for air temperature (degrees c)
These examples use Relative humidity (%): 50. They are reference calculations, not recommended settings.
Air temperature (degrees C)Dew point (degrees C)
100.046659
209.261107
4027.604458
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ToolOctopus. “Dew point calculator.” Updated 2026-09-29. https://tooloctopus.com/dew-point-calculator.
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