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Dew and Frost Point with Vapor Pressure

Calculate dew or frost point and vapor pressure using a documented ice/water saturation model, with explicit zero-humidity and range limits.

Use this result well

Inputs that matter
Air temperature (°C), Relative humidity (%), Sources and assumptions
Output to expect
Dew or frost point and vapor pressure
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

Dew or frost point and vapor pressure

Invert the ASHRAE saturation-pressure equation from simultaneous temperature and relative humidity. Report the phase convention, zero-water-vapor limit and values outside the −100 to 200°C saturation range explicitly.

e = RH × es(T) / 100; solve es(Ts) = e. ASHRAE ice/water equations meet at the triple point.

Updated: September 2026

Example Scenarios

Inspect the example and its input basis, then substitute your own documented measurements or matched cases.

Air temperature (°C): 25Relative humidity (%): 60

→ 16.701132°C dew point

Common Mistakes to Avoid

Mixing observation and model inputs

Use the exact units, timestamp, level and measurement or model basis stated by the selected mode. A similar quantity from another instrument or product is not automatically interchangeable.

Treating an illustrative case as a measurement

Replace the example with your own sourced inputs. Retain missing values and method limits, and keep raw source data alongside a saved calculation.

FAQ

Invert the ASHRAE saturation-pressure equation from simultaneous temperature and relative humidity. Report the phase convention, zero-water-vapor limit and values outside the −100 to 200°C saturation range explicitly.

Retain the station or profile identity, observation or issue/valid time, measurement units, quality flags, source and stated method. Missing values, trace precipitation and known zeros have different meanings.

Save weather case keeps an explicit local record. Copy MD includes current inputs and notes; Download CSV includes the current result breakdown. Keep portable copies separately and retain raw source data.

About Dew and Frost Point with Vapor Pressure

Invert the ASHRAE saturation-pressure equation from simultaneous temperature and relative humidity. Report the phase convention, zero-water-vapor limit and values outside the −100 to 200°C saturation range explicitly.