How the Dew Point Calculator works.
γ = ln(RH/100) + aT/(b+T); dew point = bγ/(a−γ)T is Celsius, RH is relative humidity, a = 17.625, and b = 243.04 °C for this Magnus approximation.
Worked example for the Dew Point Calculator.
At 20 °C and 50% relative humidity, the Magnus approximation gives a dew point of about 9.3 °C.
How to read this result.
Dew point is the temperature at which air with the entered moisture content would become saturated under the approximation.
How this tool gets the answer
γ = ln(RH/100) + aT/(b+T); dew point = bγ/(a−γ). T is Celsius, RH is relative humidity, a = 17.625, and b = 243.04 °C for this Magnus approximation. Dew point is the temperature at which air with the entered moisture content would become saturated under the approximation.
A useful example
At 20 °C and 50% relative humidity, the Magnus approximation gives a dew point of about 9.3 °C. A quick way to verify the calculation is: Convert to Celsius, compute gamma from temperature and the natural logarithm of relative humidity, then solve the Magnus relation for dew point.
What the result tells you
Dew point is the temperature at which air with the entered moisture content would become saturated under the approximation. Temperature may be entered in Celsius or Fahrenheit and is normalized to Celsius; relative humidity is a percentage from above zero through 100.
Where the answer can go wrong
Relative humidity at zero is outside the logarithmic formula, humidity above 100% is invalid, and extreme temperatures outside normal meteorological use are rejected. The Magnus approximation is practical for common near-surface conditions but is not a substitute for calibrated observations or specialist psychrometric calculations.
Privacy and practical use
The calculation runs locally in your browser and FigureNest does not send the entered values to a calculation service. Keep the source value and its unit with any result you save so you can reproduce the calculation later.
Inputs and edge cases to check.
Relative humidity at zero is outside the logarithmic formula, humidity above 100% is invalid, and extreme temperatures outside normal meteorological use are rejected.
What this tool does not include.
The Magnus approximation is practical for common near-surface conditions but is not a substitute for calibrated observations or specialist psychrometric calculations.
Reference guidance and methodology.
Dew Point Calculator questions.
What does the Dew Point Calculator do?
Estimate dew point from air temperature and relative humidity with the Magnus formula.
How can I check the result?
Convert to Celsius, compute gamma from temperature and the natural logarithm of relative humidity, then solve the Magnus relation for dew point.
Which units and assumptions matter?
Temperature may be entered in Celsius or Fahrenheit and is normalized to Celsius; relative humidity is a percentage from above zero through 100. The Magnus approximation is practical for common near-surface conditions but is not a substitute for calibrated observations or specialist psychrometric calculations.
Are the entered values sent or stored?
No. The calculation runs locally in your browser and FigureNest does not send or store calculator inputs.