Example
At 20 °C and 50% relative humidity, the dew point is about 9.3 °C and absolute humidity is about 8.6 g/m³.
How the estimate works
Enter air temperature and relative humidity. The calculator estimates saturation and actual vapour pressure, dew or frost point, and absolute humidity. The chart shows how absolute humidity changes across relative humidity at the same temperature.
Frequently asked questions
What is dew point?
It is the temperature at which air with the same moisture content reaches saturation as it cools. Below freezing, this calculator uses the ice-based frost-point equation.
What does absolute humidity mean?
It estimates the mass of water vapour in one cubic metre of air, in grams per cubic metre.
Does a surface below the dew point always get wet?
Not necessarily. The result indicates conditions that may allow condensation. Air movement, materials, measurement error and local conditions also matter.
Can this calculator detect mould or diagnose a building problem?
No. It only calculates an estimate from the values entered. It does not inspect a room, measure a surface or diagnose mould.
Model and limits
This is an estimate using the WMO saturation-vapour-pressure equations for water above 0 °C and ice below 0 °C. Air temperature is limited to −45 to 60 °C, and the calculated dew or frost point must remain within the equation’s published range. It assumes near-surface conditions and does not correct for pressure or instrument error. A surface at or below the calculated point may allow condensation; this is not a mould diagnosis or building inspection.