Relative Humidity Calculator

1. Select the calculation mode matching your available measurements.
2. Enter air temperature using the displayed temperature scale.
3. Provide relative humidity, dew point, or wet-bulb temperature.
4. Enter local pressure or estimate it from elevation.
5. Choose a saturation formula and water-surface setting.
6. Add surface temperature for condensation and mold assessment.
7. Set precision, uncertainty, and optional sensor corrections.
8. Press the calculation button and review every result card.
9. Export CSV, JSON, or a printable PDF report.

The comprehensive mode needs air temperature and relative humidity. Dew-point mode uses air temperature and measured dew point. Wet-bulb mode additionally needs reliable atmospheric pressure. The calculator converts units before evaluating equations. It then returns a consistent group of psychrometric properties.

Relative humidity from dew point

The dew point identifies the vapor pressure already present. Saturation pressure at air temperature identifies the maximum possible vapor pressure. Their ratio gives relative humidity.

Actual vapor pressure

Actual vapor pressure supports dew point, absolute humidity, humidity ratio, enthalpy, and condensation calculations.

Absolute humidity

Here, vapor pressure uses hectopascals. Temperature uses degrees Celsius inside the Kelvin conversion.

Humidity ratio

The humidity ratio compares water-vapor mass with dry-air mass. Both pressures must use identical units.

Specific humidity

Specific humidity compares vapor mass with total moist-air mass. It changes less directly with air temperature.

Wet-bulb humidity calculation

This relation accounts for evaporative cooling and atmospheric pressure. A ventilated and wetted sensor improves measurement quality.

Relative humidity changes with temperature

Relative humidity describes current vapor pressure compared with saturation pressure. Warm air has a higher saturation pressure. Therefore, warming unchanged air lowers relative humidity. Cooling unchanged air raises relative humidity. The actual vapor amount can remain constant during both changes.

Dew point tracks actual moisture

Dew point is the temperature where saturation begins. A high dew point indicates abundant atmospheric moisture. A low dew point indicates drier air. Dew point often supports comfort discussions better than relative humidity because normal temperature changes affect it less.

Wet-bulb temperature shows evaporative potential

A wet surface cools as water evaporates. The wet-bulb temperature represents the cooling limit under current conditions. Dry air creates stronger evaporation and a larger dry-bulb difference. Humid air produces a smaller difference.

Pressure matters for psychrometric work

Atmospheric pressure changes the mass relationship between water vapor and dry air. Humidity ratio, specific humidity, enthalpy, and wet-bulb calculations need pressure. Station pressure is usually better than sea-level corrected pressure for local air calculations.

Surface humidity predicts condensation

Air touching a cold surface cools locally. Its relative humidity rises as saturation pressure falls. Condensation begins when surface temperature reaches the dew point. Mold can become possible before visible water appears. Long exposure near high surface humidity deserves attention.

Indoor comfort and health

Very dry air can increase static electricity and discomfort. Excess humidity can make warm rooms feel hotter. It may also support dust mites and mold. Many buildings target a moderate indoor range. Local climate and construction still affect suitable settings.

Heating, ventilation, and cooling

HVAC professionals use humidity ratio and enthalpy for load calculations. Cooling coils remove sensible and latent heat. Their surface temperature can fall below dew point. That creates condensate and lowers moisture content. Heating alone changes relative humidity without removing vapor.

Agriculture and greenhouses

Vapor pressure deficit describes atmospheric drying demand. Plants generally transpire faster when deficit rises. Very low deficit can slow moisture movement. High deficit can stress plants. Crop stage, light, airflow, and leaf temperature also matter.

Museums, archives, and storage

Paper, wood, textiles, and coatings exchange moisture with surrounding air. Fast humidity changes can cause dimensional movement. Sustained high humidity supports biological damage. Monitoring should include temperature, humidity, and exposure duration.

Industrial and laboratory processes

Drying, coating, printing, electronics, and calibration work can depend on moisture. Absolute measures often support mass balances. Relative humidity remains valuable for material equilibrium and surface behavior. Sensor placement should represent the actual process zone.

Weather observation

Weather stations commonly report temperature, humidity, dew point, and pressure. Shielding protects sensors from direct radiation. Ventilation improves response. Calibration and maintenance reduce drift. Comparisons should use measurements taken at similar heights and times.