Humidity Converter
Convert between relative humidity, dew point, and absolute humidity using air temperature.
Useful for HVAC, weather, and indoor climate control.
Enter air temperature and one humidity value — the others calculate automatically.
Humidity conversions require knowing the air temperature because the capacity of air to hold moisture changes with temperature.
Key terms:
- Relative Humidity (RH%): The percentage of moisture in the air compared to the maximum it can hold at that temperature. 50% RH means the air holds half its maximum capacity.
- Dew Point: The temperature at which the air becomes fully saturated and water begins to condense. A higher dew point means more moisture in the air.
- Absolute Humidity: The actual mass of water vapor per cubic meter of air, measured in grams per cubic meter (g/m3).
Saturation vapor pressure formula (Magnus-Tetens approximation):
- Es(T) = 6.1078 x 10^(7.5 x T / (237.3 + T)) in hectopascals (hPa)
- Where T is the air temperature in degrees Celsius
Dew point from relative humidity:
- gamma = ln(RH/100) + (7.5 x T) / (237.3 + T)
- Td = 237.3 x gamma / (7.5 - gamma)
Absolute humidity from RH and temperature:
- AH = (2.1674 x Es(T) x RH / 100) / (273.15 + T) in g/m3
Comfort level reference table:
| Condition | RH% Range | Dew Point Range |
|---|---|---|
| Too dry | Below 30% | Below 0C (32F) |
| Comfortable | 30-60% | 4-16C (40-60F) |
| Humid | 60-80% | 16-21C (60-70F) |
| Oppressive | Above 80% | Above 21C (70F) |
Practical tips for everyday use:
- Indoor comfort is typically 40-60% RH at 20-22C (68-72F).
- Dew point is a better indicator of how muggy it feels than relative humidity alone.
- A dew point above 18C (65F) feels noticeably humid to most people.
- At 100% RH, the dew point equals the air temperature exactly.
- Cold air holds much less moisture, so winter air often feels very dry indoors after heating.