Measure air dryness using temperature and humidity. See saturation pressure, vapor pressure, and deficit instantly. Export clean reports and graphs for rapid field decisions.
| Case | Air Temp (°C) | Surface Temp (°C) | RH (%) | Pressure (kPa) | Humidity Deficit (kPa) | Meaning |
|---|---|---|---|---|---|---|
| Cool room | 20 | 20 | 40 | 101.325 | 1.4030 | Strong drying demand |
| Humid room | 25 | 25 | 75 | 101.325 | 0.7923 | Moderate drying demand |
| Warm leaf | 25 | 28 | 60 | 101.325 | 1.5921 | Extra evaporation from warmer surface |
| Cool surface | 25 | 20 | 95 | 101.325 | -0.3101 | Possible condensation or moisture surplus |
These example values illustrate common patterns. Your result changes with temperature, relative humidity, pressure, and any surface temperature difference.
The calculator uses a Magnus-style saturation vapor pressure equation in kilopascals. Relative humidity converts saturation pressure into actual vapor pressure. The deficit is the remaining pressure gap.
When the surface temperature differs from the air temperature, the calculator uses the surface value for saturation pressure. That makes the result more useful for leaves, cold walls, wet materials, and evaporation studies.
A negative value means the surface is cooler than the air moisture state can support, which suggests condensation or a moisture surplus at that surface.
Humidity deficit is the gap between saturation vapor pressure and actual vapor pressure. It shows how strongly air or a surface can drive evaporation. Larger values usually mean faster drying and stronger moisture demand.
Surface temperature changes saturation vapor pressure. A warm leaf, wet slab, or heated material can evaporate faster than the surrounding air suggests. A cool surface can even shift the result below zero and indicate condensation risk.
In many practical settings, yes. Both describe the pressure difference between saturation and actual moisture conditions. This page uses the term humidity deficit while also showing an air-only deficit and a surface-adjusted deficit.
A negative result means the actual vapor pressure is higher than the saturation pressure at the chosen surface temperature. That usually signals moisture surplus, fogging, or condensation potential on that cooler surface.
Use your local atmospheric pressure in kilopascals if available. If you do not have a measured value, standard sea-level pressure of 101.325 kPa is a reasonable default for many classroom and general engineering calculations.
Higher relative humidity raises actual vapor pressure, so the remaining gap to saturation shrinks. That reduces the drying demand. If the curve crosses below zero, the chosen surface conditions favor condensation instead of evaporation.
Leave it blank when you want a standard air-based deficit and do not have a separate surface measurement. The calculator will automatically set the surface equal to the air temperature and compute the usual atmospheric deficit.
Yes. The method is useful for plant environments, HVAC checks, drying processes, storage analysis, and surface condensation studies. Just remember that airflow, radiation, and material properties also influence real evaporation rates.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.