Select “Solve for”
Choose Temperature, Relative humidity or Dew point. The selected card becomes the calculated value.
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THERMO / 035
Dew Point Calculator
Explore temperature, relative humidity and dew point as one linked air state. Choose any value to calculate and use live sliders to see condensation and moisture-risk results immediately.
Any two values°C / °FCondensation risk
ENGINEERING CONTEXT
Use the number as a physical check—not as a hidden property lookup.
Dew point is the temperature at which the current water-vapor content reaches saturation. It links the air state directly to window fogging, cold-duct sweating and moisture on cooled components.
01
Define the thermodynamic state. Keep pressure, temperature, composition and humidity basis explicit.
02
Calculate with visible assumptions. The tool reports the governing engineering relation and its range limitations.
03
Compare with the CFD or system model. Large disagreement is a diagnostic signal—not something to average away.
RELATED ENGINEERING PATH
Continue from property check to diagnosis or project-specific support.
Abecator connects calculators to the technical and consulting context around the result.
HOW TO USE IT
Choose the unknown, then adjust the two values you know.
Temperature, relative humidity and dew point remain thermodynamically linked. Every result updates immediately.
Enter the known state
Type exact values or move the sliders. Switch between Celsius and Fahrenheit without changing the physical state.
Check a surface
Enter a wall, window, duct, windshield, pipe or coil temperature. A zero or negative margin means condensation is possible.
Read the indicators
Use vapor pressure and humidity ratio for engineering checks. Environmental tiles are broad screening indicators.
What dew point means
Dew point is the temperature to which air must be cooled, at essentially constant pressure and water-vapor content, before it becomes saturated. Relative humidity changes with temperature; dew point stays nearly constant while moisture content stays constant.
If a surface is colder than the dew point, moisture can condense. Practical designs should retain extra margin for sensor uncertainty, thermal bridges and local cold spots.
Method and formula
The calculator uses a Magnus-type saturation-vapor-pressure relation and its inverse. For dew point it evaluates γ = ln(RH/100) + aT/(b + T) and Tdew = bγ/(a − γ), with an ice-aware saturation relation below 0 °C.
Humidity ratio uses standard pressure, 101.325 kPa. Surface RH is the RH that the same vapor content produces at the chosen surface temperature.
How to interpret the margin
- Margin > 0: no bulk-air condensation is predicted.
- Margin ≤ 0: the surface is at or below dew point.
- Mold, corrosion and material response also depend on time, contamination, ventilation and repeated cycles.
- This screening tool does not predict condensation rate.
Example
At 22 °C and 60% RH, dew point is about 14 °C. A 12 °C window or duct is below that value, so condensation is possible. Raise the surface temperature, reduce moisture content, or both.
Interaction inspired by the Image Permanence Institute’s Dew Point Calculator; the wording and engineering interpretation here are original to Abecator CFD.