Calculation sequence
Step-by-step method
- Calculate saturation vapor pressure at dry-bulb temperature.
- Multiply by relative humidity for actual vapor pressure.
- Invert the vapor-pressure correlation for dew point.
MechanicalIntermediatePsychrometrics
Dew-Point Calculator
Estimate air dew-point temperature from dry-bulb temperature and relative humidity.
Why it matters: Dew point governs surface-condensation risk and moisture-control decisions.
Calculated result
Engineering evaluation
Estimated dew-point temperature (Tdp)55.05 °F
- Entered dry-bulb temperature (Tdb)
- 75 °F
- Entered relative humidity (RH)
- 50 %
Engineering interpretation
Estimated air dew point is 55.05 °F.
Important limitations
- Sensor uncertainty and local moisture/temperature gradients can materially affect condensation evaluation.
Engineering knowledge center
Understand the calculation—not just the answer
Governing relationships
Tdp = f(Tdb,RH) using saturation-vapor-pressure correlation
Current substitution
At Tdb = 75 °F and RH = 50%, Tdp = 55.05 °F.
Equation legend
Inputs and calculated quantities
- Tdb
- Dry-bulb temperature — °F or °C
- RH
- Relative humidity — %
- Tdp
- Estimated dew-point temperature — °F
- Tdb
- Entered dry-bulb temperature — °F
- RH
- Entered relative humidity — %
Applications
How this calculation is used
Building design
Screen envelope, piping, and HVAC surface temperatures.
Construction
Check temporary-condition moisture risks.
Commissioning
Convert field dry-bulb and relative-humidity readings to dew point.
Quality controls
Assumptions and limitations
Assumptions
- Entered values represent one stable operating condition and use consistent measurement boundaries.
- Fluid and air properties are representative of the evaluated condition.
Limitations
- This is a preliminary evaluation and field-verification tool, not a final sizing or code-compliance determination.
- Manufacturer data, adopted codes, project criteria, and professional engineering review remain controlling.
Field use
Verification procedure
- Confirm measurement boundaries, operating mode, and instrument calibration.
- Stabilize the system and record simultaneous readings.
- Compare the calculation with project requirements and manufacturer data before disposition.
Common engineering mistakes
- Mixing values from different operating conditions.
- Using nominal rather than measured flow, temperature, power, or fluid properties.
Technical basis
References and source standards
- ASHRAE Handbook—FundamentalsPsychrometrics, heat transfer, load relationships, and HVAC calculation context; verify the licensed current edition during professional review.
Engineering calculation disclaimer
These engineering tools are provided for educational, preliminary evaluation, field verification, and commissioning support. Results depend on the accuracy of user-entered information and the assumptions stated for each calculation. Every colored status and comparison is a screening indicator only; project criteria, contract requirements, applicable codes, manufacturer instructions, measurement uncertainty, and authorized engineering judgment govern. The tools do not replace project-specific engineering analysis or the judgment of a licensed professional engineer.
Read the full use and limitation statement