Vapor Pressure Calculator

Compare vapor-pressure values alongside dew point, relative humidity, absolute humidity and humidity ratio without uploading data.

Vapor-pressure inputs

Use relative humidity, or enter a dew point to derive actual vapor pressure directly from saturation vapor pressure at the dew point.

Air temperature (°C)

Relative humidity (%)

Optional dew point (°C)

Psychrometric Calculator Dew Point Relative Humidity Absolute Humidity Wet Bulb

Pressure relationship

—Saturation vapor pressure

—Actual vapor pressure

—Vapor-pressure deficit

—Derived RH

One moist-air state, several related properties

Relative humidity, dew point, wet bulb, vapor pressure, absolute humidity and humidity ratio describe different parts of the same moisture state. WebToolArc keeps the selected inputs visible and shows related outputs together instead of treating the terms as interchangeable.

Accuracy boundary

These browser calculations use standard psychrometric approximations. Real measurements can differ because of sensor calibration, station pressure, ventilation, radiation, local gradients and the exact saturation-vapor-pressure formulation. Use calibrated instruments and applicable engineering or meteorological standards when decisions require certified measurements.

Usage notes optional

Humidity relationships depend on the model and temperature range

Relative humidity, saturation vapor pressure, dew point, and actual vapor pressure are linked but not interchangeable. A result derived from one empirical saturation-pressure approximation should be kept with the temperature range and coefficients that produced it.

Do not treat moist-air properties as a weather forecast

This browser calculation describes a local thermodynamic state from entered values. Pressure, ventilation, sensor accuracy, rapid temperature changes, condensation on real surfaces, and outdoor weather evolution can all differ from the simplified state calculation.

Check whether dew point or relative humidity is the measured quantity

A humidity sensor may report relative humidity directly, while another workflow may start from dew point. Those are different inputs to the moist-air relationship and they carry different measurement uncertainty. If both are available, compare the implied vapor pressure instead of mixing values from different times or locations; a small temperature shift can materially change saturation pressure.

Keep sensor time and location aligned

Temperature and humidity readings taken at different times, heights, or rooms may describe different air masses. When using the result to assess condensation or HVAC conditions, pair measurements from the same location and time window and include sensor tolerance in the interpretation.