Relative Humidity Calculator
Calculate relative humidity from dry bulb and wet bulb temperatures.
Supports Fahrenheit and Celsius with psychrometric formulas.
Relative Humidity
Relative humidity is the ratio of the current amount of water vapor in the air to the maximum amount the air can hold at that temperature.
RH = (Actual Vapor Pressure / Saturation Vapor Pressure) × 100%
Using wet and dry bulb temperatures:
The saturation vapor pressure is calculated with the Magnus formula:
e(T) = 6.112 × exp((17.67 × T) / (T + 243.5))
Where T is temperature in °C. The actual vapor pressure from wet bulb:
e_actual = e(T_wet) − 0.000799 × P × (T_dry − T_wet)
Where P is atmospheric pressure (default 1013.25 hPa at sea level).
Comfort ranges:
- 30–50%: Ideal indoor comfort range
- Below 30%: Dry — may cause irritation, static electricity
- Above 60%: Humid — mold risk, discomfort
- Above 80%: Very humid — condensation likely
Key facts:
- Warm air can hold more moisture than cold air
- The wet bulb is always ≤ the dry bulb temperature
- When wet = dry bulb, humidity is 100%