Absolute Humidity Estimator
Absolute humidity estimates the mass of water vapour contained in a unit volume of air. Here vapour pressure is approximated from temperature and relative humidity.
How to use this calculator
- Enter air temperature (°c), relative humidity (%) using the same measurement window and units.
- Check the result and intermediate values, then change one input at a time when comparing scenarios.
- Keep the stated scope and assumptions attached to any result you share.
Formula and method
Saturation pressure eₛ ≈ 6.112 × exp(17.67T/(T+243.5)); actual vapour pressure = RH × eₛ; absolute humidity ≈ 216.7e/(T+273.15) g/m³.
- The estimator gives approximately 10.7 g/m³ of water vapour.
- This simplified method assumes standard atmospheric use of the empirical vapour-pressure relation. It is not a calibrated HVAC instrument or safety assessment.
Worked examples
Worked example
22°C air at 55% relative humidity.
The estimator gives approximately 10.7 g/m³ of water vapour.
The estimator gives approximately 10.7 g/m³ of water vapour.
Understanding the result
The estimator gives approximately 10.7 g/m³ of water vapour.
This simplified method assumes standard atmospheric use of the empirical vapour-pressure relation. It is not a calibrated HVAC instrument or safety assessment.
Important notes
This simplified method assumes standard atmospheric use of the empirical vapour-pressure relation. It is not a calibrated HVAC instrument or safety assessment.
Use measured inputs or documented assumptions, and validate important decisions with the appropriate source specifications or professional guidance.
Frequently asked questions
Does absolute humidity change if air warms?
At unchanged water-vapour mass, volume and pressure effects matter; this estimate recalculates based on entered state.
Can I use this to size ventilation?
Use suitable ventilation design methods and local requirements rather than this single humidity estimate.
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This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.