Dew Point Calculator
Enter air temperature and relative humidity to calculate the dew point instantly.
Tip: Relative humidity should be between 1 and 100.
What Is Dew Point?
Dew point is the temperature at which air becomes fully saturated with water vapor and condensation begins. When the air cools to its dew point, moisture can form as dew, fog, or condensation on surfaces. Unlike relative humidity, dew point gives a more direct measure of how much moisture is actually in the air.
If you want to calculate the dew point for weather, indoor air comfort, HVAC work, or greenhouse control, this metric is one of the best indicators of real atmospheric moisture.
Dew Point vs. Relative Humidity
Relative Humidity Changes With Temperature
Relative humidity (RH) depends on both moisture content and temperature. That means RH can change throughout the day even if the amount of water vapor stays the same.
Dew Point Reflects Absolute Moisture
Dew point stays more stable unless moisture is added or removed. A higher dew point means there is more water vapor in the air, regardless of whether it's morning or afternoon.
- Low dew point: Dry air, less sticky feeling
- High dew point: Moist air, muggy or oppressive feeling
How to Calculate the Dew Point
This page uses the Magnus formula, a common and reliable approximation for everyday conditions.
Formula (Celsius)
γ = ln(RH/100) + (a × T) / (b + T)
Dew Point = (b × γ) / (a − γ)
Where:
- T = air temperature in °C
- RH = relative humidity in %
- a = 17.625
- b = 243.04
If you enter Fahrenheit, the calculator converts to Celsius, computes dew point, then converts back.
How to Interpret Your Result
- Below 10°C (50°F): Dry and generally comfortable
- 10–16°C (50–61°F): Comfortable for most people
- 16–18°C (61–64°F): Slightly humid
- 18–21°C (64–70°F): Muggy
- 21–24°C (70–75°F): Very humid
- Above 24°C (75°F): Oppressive and sticky conditions
Why Dew Point Matters
1. Weather and Outdoor Planning
Dew point helps explain how the weather will feel. Two days at the same temperature can feel very different when dew point changes. Runners, hikers, and athletes often use dew point to estimate heat stress.
2. HVAC and Indoor Comfort
In buildings, dew point affects condensation risk on ducts, windows, and walls. Maintaining the right indoor dew point can improve comfort and reduce mold potential.
3. Agriculture and Greenhouses
Growers monitor dew point to reduce fungal disease risk and optimize transpiration. It is especially helpful when controlling nighttime greenhouse climate.
4. Industrial and Technical Processes
Compressed air systems, data centers, and manufacturing lines often require strict moisture control. Dew point measurement is critical for product quality and equipment reliability.
Example
Suppose air temperature is 30°C and relative humidity is 70%. The dew point is approximately 24°C (about 75°F). That indicates very humid air and a strong chance of condensation if nearby surfaces are cooler than that value.
Tips for Better Accuracy
- Use a calibrated temperature and humidity sensor.
- Avoid direct sunlight on the sensor when measuring outdoor air.
- Allow sensors time to stabilize before recording values.
- For extreme conditions, use professional psychrometric tools for validation.
Quick FAQ
Is dew point the same as “feels like” temperature?
No. “Feels like” combines temperature, humidity, and often wind. Dew point only describes moisture content.
Can dew point be higher than air temperature?
Under normal atmospheric conditions, dew point is not higher than air temperature. At 100% RH, dew point equals air temperature.
What dew point is considered uncomfortable indoors?
Many people begin to notice discomfort above roughly 16–18°C (61–64°F) indoors, though comfort varies by person and activity.
Use the calculator above whenever you need to quickly calculate the dew point and understand moisture conditions with confidence.