Absolute Humidity Calculator
Calculate absolute humidity from temperature and relative humidity. Find moisture content in grams per cubic meter for HVAC, weather, and climate analysis.
Relative Humidity Calculator
Calculate relative humidity from dry-bulb + wet-bulb, dew point, or absolute humidity. Find RH, humidity ratio, dew point, and enthalpy.
°C
°C
kPa
Relative Humidity⧉
53.5%
Comfortable range
Humidity Ratio⧉
8.81 g/kg
Moisture per kg dry air
Dew Point (°C)⧉
12.1
Condensation temperature
Absolute Humidity⧉
10.39 g/m³
Moisture per m³ of air
Vapor Pressure⧉
1.416 kPa
Sat: 2.644 kPa
Enthalpy⧉
44.54 kJ/kg
Moist air total heat
Humidity Scale
54
0% (Dry)30%60%100% (Saturated)
| RH (%) | W (g/kg) | Dew Point (°C) | Vapor Pressure (kPa) |
|---|---|---|---|
| 10% | 1.63 | -11.0 | 0.264 |
| 20% | 3.26 | -2.0 | 0.529 |
| 30% | 4.91 | 3.6 | 0.793 |
| 40% | 6.56 | 7.8 | 1.058 |
| 50% | 8.22 | 11.1 | 1.322 |
| 60% | 9.89 | 13.9 | 1.586 |
| 70% | 11.57 | 16.3 | 1.851 |
| 80% | 13.26 | 18.4 | 2.115 |
| 90% | 14.96 | 20.3 | 2.379 |
| 100% | 16.66 | 22.0 | 2.644 |
Planning notes, formulas, and examples
About the Relative Humidity Calculator
The **Relative Humidity Calculator** determines RH from several common input pairs: dry-bulb and wet-bulb temperatures, dry-bulb and dew point, or dry-bulb and absolute humidity. Relative humidity is the ratio of actual water-vapor pressure to saturation vapor pressure at the same temperature, expressed as a percentage.
RH affects comfort, building durability, electronics reliability, and many industrial processes. The same RH value can feel very different at different temperatures because warm air can hold much more moisture than cold air.
This calculator uses the August-Roche-Magnus approximation for saturation vapor pressure and returns humidity ratio, dew point, absolute humidity, vapor pressure, and enthalpy together with a simple comfort assessment.
When This Page Helps
Humidity is easy to misread if you only look at one number. RH, dew point, and absolute humidity answer different questions, and each one matters in different jobs such as HVAC balancing, weather monitoring, storage, and environmental control.
Putting the modes together on one page helps you move from the measurement you have to the property you actually need.
How to Use the Inputs
- Select the input method: wet-bulb, dew point, or absolute humidity.
- Enter the dry-bulb (ambient) temperature.
- Enter the second measurement based on your selected method.
- Adjust barometric pressure for non-sea-level locations.
- Use presets for common weather conditions.
- Check the humidity scale visual for comfort zone indication.
- Explore the reference table for properties at different RH levels.
Formula used
Pws = 0.61078 × exp(17.27 × T / (T + 237.3)) [Magnus formula]
From wet-bulb: Pw = Pws(Twb) − 0.000662 × P × (Tdb − Twb)
From dew point: Pw = Pws(Tdp)
RH = (Pw / Pws(Tdb)) × 100%Example Calculation
Result: 53.6% RH
Pws(22°C) = 2.643 kPa, Pws(16°C) = 1.818 kPa. Pw = 1.818 − 0.000662 × 101.325 × 6 = 1.416 kPa. RH = 1.416/2.643 × 100 = 53.6%. The 6°C wet-bulb depression indicates moderate humidity in the comfortable range.
Tips & Best Practices
- Wet-bulb depression is the quickest field indicator of humidity level.
- Dew point is more intuitive than RH for condensation risk — if surface temp is at or below dew point, condensation forms.
- Winter indoor RH often drops below 20% without humidification — bad for wood, instruments, and health.
- For accurate wet-bulb measurement, ensure good airflow over the wet wick (>3 m/s).
- Mold typically starts growing above 60% RH sustained for 48+ hours.
- Electronics are best stored at 30-50% RH to prevent corrosion and static damage.
Understanding Relative Humidity
Relative humidity is expressed as a percentage, but its meaning is often misunderstood. RH = 50% means the air contains half the maximum vapor it could hold at the current temperature — not half of some absolute scale. Because warm air can hold exponentially more moisture than cold air, the same RH at different temperatures represents vastly different amounts of actual water.
At 30°C, saturated air (100% RH) holds about 30.4 g/m³ of water vapor. At 10°C, saturated air holds only 9.4 g/m³. So 50% RH at 30°C (15.2 g/m³) contains more than 100% RH at 10°C — which is why tropical air feels so much more humid than maritime temperate air even at the same RH reading.
Measurement Methods
**Sling Psychrometer:** Two thermometers (dry and wet) whirled through air. Simple, reliable, and self-calibrating. Still used for HVAC commissioning and weather station checks.
**Capacitive Sensors:** Modern electronic humidity sensors use a polymer film whose capacitance changes with moisture absorption. Accurate to ±2-3% RH, these dominate in commercial HVAC controllers and weather stations.
**Chilled Mirror Hygrometer:** The gold standard for laboratory accuracy (±0.1°C dew point). A mirror is cooled until condensation forms; the mirror temperature at the onset of condensation equals the dew point. Used for calibrating other instruments.
Industrial and Agricultural Applications
Food storage requires precise humidity control — too dry causes shrinkage and weight loss, too humid promotes mold and bacterial growth. Grain storage typically targets 60-65% RH. Cheese aging rooms maintain 85-95% RH. Pharmaceutical clean rooms require 30-50% RH to prevent both microbial growth and electrostatic discharge.
Sources & Methodology
Last updated:
Frequently Asked Questions
The comfortable range for most people is 30-60% RH. Below 30% causes dry skin, static electricity, and respiratory irritation. Above 60% promotes mold growth, dust mites, and a feeling of stuffiness.
At 30°C and 80% RH, there is much more absolute moisture (about 24 g/m³) than at 10°C and 80% RH (about 7.5 g/m³). The heat index combines temperature and moisture to reflect how humid heat actually feels to humans.
Technically, supersaturation can occur briefly (RH slightly above 100%) before condensation begins. In practice, weather instruments cap at 100%. Fog and clouds form at or very near 100% RH.
RH is a percentage (actual/maximum moisture at that temperature). Absolute humidity (g/m³) is the actual mass of water vapor per volume. RH depends on temperature; absolute humidity does not.
Lower atmospheric pressure at altitude affects vapor pressure calculations. The psychrometric coefficient changes, and wet-bulb measurements require barometric pressure correction. Enter the local pressure for valid inputs.
The difference between dry-bulb and wet-bulb temperatures. Greater depression = drier air. At 0 depression (Tdb = Twb), the air is saturated at 100% RH.
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