01
Choose an independent moisture input
Dry bulb plus dew point is a strong pair when a chilled-mirror or derived dew-point reading is available. Dry bulb plus humidity ratio suits mass balances. The default focused pair reconstructs RH from dry bulb and dew point without treating two dependent moisture measures as independent evidence.
Relative humidity is actual vapor pressure divided by saturation vapor pressure at the same dry bulb. It therefore changes when temperature changes even if no water enters or leaves the air.
02
Verified example
At 25 °C dry bulb and 13.864 °C dew point at 101.325 kPa, the result is 50.000% RH. The connected state is 9.883 g/kg humidity ratio and 50.326 kJ/kg enthalpy. The calculator keeps full internal precision, so entering a rounded dew point may produce a result a few hundredths from 50%.
If that air is sensibly heated to 40 °C at unchanged humidity ratio, RH falls to 28.754% while moisture mass is unchanged. That distinction matters when diagnosing over-dry complaints after heating.
03
Use RH for the right decision
RH is useful for comfort context, material response and proximity to saturation at the current temperature. Use dew point for cold-surface risk and humidity ratio for moisture addition or removal. Use more than one property when a diagnosis crosses those decisions.
Trend dry bulb and RH together. A rising RH trace can mean added moisture, falling temperature, or both; the complete state shows which explanation fits.
04
Mistakes and measurement effects
Do not interpret 60% RH at 20 °C as more water than 40% RH at 30 °C without calculating humidity ratio. Do not accept values above 100% as ordinary humid air; the form reports an error and moves focus to the invalid field.
Probe self-heating, wall placement, slow response and temperature calibration can dominate the derived RH. The calculation assumes one uniform equilibrium state and cannot correct a poor sampling location.
05
Limits and next workflow
The model uses documented water/ice saturation relations within its stated range. It does not predict comfort, microbial growth or material equilibrium by itself. Those outcomes require exposure time, surface conditions and the applicable guidance.
Use the airside comparison reference to separate temperature-driven RH change from real moisture change, then record humidity ratio at each location.