The moisture question answered by Actual Vapor Pressure
Convert temperature and relative humidity into the partial pressure of water vapor.
Actual vapor pressure measures water vapor’s contribution to total air pressure. Relative humidity supplies the fraction of saturation present at the entered temperature.
Actual Vapor Pressure begins with air temperature, relative humidity. Classify each entry as measured, forecast, assumed, or derived before treating actual vapor pressure as an observation.
Collecting compatible inputs for Actual Vapor Pressure
Use temperature and humidity observed together. A humidity percentage from before a rapid temperature change will not describe the later state unless vapor content remained unchanged and the percentage was recalculated.
Write the location, elevation or pressure level, timestamp, time zone, instrument exposure, and data source beside the Actual Vapor Pressure output. These identifiers often explain a disagreement in actual vapor pressure more effectively than another decimal place.
How Actual vapor pressure is calculated
The working relationship is Relative humidity ÷ 100 × saturation vapor pressure. The browser applies only the displayed values, so the Actual Vapor Pressure result can be repeated without an account or hidden weather feed.
Keep the unrounded Actual Vapor Pressure output through any later moisture conversion. Round actual vapor pressure according to sensor resolution and the purpose of the record, not simply the number of digits the page can display.
A worked check before entering field data
Start with the values already displayed and repeat Relative humidity ÷ 100 × saturation vapor pressure independently. Then alter one Actual Vapor Pressure input in a direction with a predictable moisture effect and confirm the result responds accordingly.
Reset restores the Actual Vapor Pressure demonstration values. It does not contact a station, preserve an earlier entry, or decide whether the source observation passed quality control.
Where the Actual Vapor Pressure model stops
The saturation relationship is approximate and switches form in rigorous work over ice. Sensor error and unrepresentative exposure remain more important than displaying many decimal places.
Actual Vapor Pressure provides a documented moisture calculation rather than a forecast, warning, equipment specification, health assessment, or authorization to operate in hazardous weather.
Retaining an auditable Actual Vapor Pressure record
Save the original observations, conversions, formula version, full-precision output, final rounded value, and any quality flags with the Actual Vapor Pressure record. A reviewer should not need to infer which definition or saturation phase produced actual vapor pressure.
When a source value, site, interval, pressure basis, or method changes, create a new dated Actual Vapor Pressure result rather than replacing the earlier evidence.
Units and boundary cases in Actual Vapor Pressure
Actual Vapor Pressure reports hPa. Follow every source unit through the equation; pressure values must share a scale, and temperatures must use the scale specified beside their fields.
For Actual Vapor Pressure, test an appropriate boundary such as saturation, equal temperatures, zero qualifying intervals, or unchanged temperature. A boundary result can expose reversed subtraction, percent entered as a fraction, or pressure entered in the wrong unit.
Saturation over water and ice in Actual Vapor Pressure
The saturation reference used by Actual Vapor Pressure belongs with the answer. Below freezing, a water-based and ice-based relationship can produce different values even when the observation is unchanged.
Do not splice coefficient sets midway through a Actual Vapor Pressure series without documenting the change. Consistent convention is essential when small differences in actual vapor pressure matter.
To extend the Actual Vapor Pressure record into a related humidity question, open the Wet-Bulb Depression Calculator.
Checking sensitivity of Actual vapor pressure
Change the least certain Actual Vapor Pressure input across a credible measurement range while holding the other entries fixed. Record how much actual vapor pressure moves and whether that movement changes the intended interpretation.
The controlled Actual Vapor Pressure range is not a probability interval. It shows formula sensitivity to selected inputs; it does not model all weather uncertainty or guarantee that the true atmosphere lies inside the tested limits.
Interpreting Actual vapor pressure without changing its meaning
Actual vapor pressure is an intermediate quantity for dew point, mixing ratio, specific humidity, and vapor-pressure deficit. Carry extra digits when it feeds those calculations.
Compare two Actual Vapor Pressure results only after aligning temperature scale, pressure basis, saturation phase, observation height, averaging window, and rounding convention.
Carrying Actual vapor pressure into another calculation
If another weather tool needs actual vapor pressure, transfer the unrounded number with its unit and source time. State whether it came directly from an instrument or was derived by Actual Vapor Pressure.
A single Actual Vapor Pressure result summarizes one defined state. A trend requires repeated, comparable records and a method for gaps, relocations, sensor changes, and corrections.
To extend the Actual Vapor Pressure record into a related humidity question, open the Relative Humidity After Temperature Change Calculator.
Common questions about Actual vapor pressure
Why could another humidity source disagree?
Another Actual Vapor Pressure source may use different coefficients, saturation phase, pressure, station exposure, observation timing, or rounding.
How can I verify actual vapor pressure?
Repeat Relative humidity ÷ 100 × saturation vapor pressure with the recorded inputs and test one controlled change whose direction is physically clear.
When should the calculation be repeated?
Create a new Actual Vapor Pressure result when its location, time, input, pressure basis, instrument, or formula convention changes.
Does this page provide a weather warning?
No. Actual Vapor Pressure performs local arithmetic and does not replace current forecasts, observations, watches, warnings, or operating rules.