Dew Point Calculator
Calculate dew point temperature instantly from air temperature and relative humidity using the Magnus-Tetens formula. Understand comfort levels, frost point, and plan outdoor activities with our free dew point calculator.
About This Calculator
The Dew Point Calculator helps you determine the temperature at which water vapor in the air begins to condense into dew. Understanding the dew point is essential for assessing human comfort, planning outdoor activities, managing HVAC systems, and predicting weather conditions like fog and frost. Unlike relative humidity, dew point provides an absolute measure of moisture in the air that does not fluctuate with temperature changes.
Our calculator uses the Magnus-Tetens formula (Alduchov & Eskridge, 1996) with coefficients a = 17.625 and b = 243.04°C to compute the dew point from air temperature and relative humidity. The formula is accurate to within ±0.35°C for temperatures ranging from -40°C to 50°C. When the dew point falls below freezing, the calculator also computes the frost point using the appropriate ice-surface coefficients.
Dew Point Comfort Scale
- Below 10°C (50°F): A bit dry for some — common in winter or arid climates
- 10-16°C (50-60°F): Dry and comfortable — ideal indoor and outdoor conditions
- 16-18°C (60-65°F): Getting sticky — noticeable moisture in the air
- 18-21°C (65-70°F): Unpleasant — lots of moisture, feels humid
- Above 21°C (70°F): Oppressive — difficult to cool down, dangerous above 24°C
Practical Applications
- Weather Forecasting: Predict fog, frost, and precipitation likelihood
- Aviation: Assess carburetor icing and visibility conditions
- Agriculture: Manage greenhouse humidity to prevent fungal diseases
- HVAC: Design comfortable indoor environments with proper dehumidification
- Outdoor Planning: Determine if conditions are safe for sports and activities
Frequently Asked Questions
What is dew point?
Dew point is the temperature at which water vapor in the air begins to condense into liquid water (dew). When the air temperature drops to the dew point, the relative humidity reaches 100% and moisture starts forming on surfaces. It is a direct measure of the moisture content in the air, unlike relative humidity which depends on temperature.
How is dew point calculated?
Dew point is calculated using the Magnus-Tetens formula: Td = (b × α(T,RH)) / (a - α(T,RH)), where α(T,RH) = ln(RH/100) + (a × T) / (b + T), a = 17.625, b = 243.04°C, T is air temperature in Celsius, and RH is relative humidity in percent. This formula is accurate to ±0.35°C for temperatures from -40°C to 50°C.
What is a comfortable dew point?
Dew point comfort levels: below 10°C (50°F) feels a bit dry; 10-16°C (50-60°F) is dry and comfortable; 16-18°C (60-65°F) feels sticky; 18-21°C (65-70°F) is unpleasant with lots of moisture; above 21°C (70°F) is oppressive and can be dangerous above 24°C (75°F). In India (high humidity), dew points of 20-25°C are common in summer causing discomfort. In the US and UK, dew points above 21°C trigger heat advisories.
What is the difference between dew point and relative humidity?
Dew point is an absolute measure of moisture in the air, while relative humidity is a ratio of current moisture to the maximum possible at that temperature. Dew point does not change with temperature (only moisture content), whereas relative humidity changes as temperature fluctuates. A 65°F day with 50% humidity feels more humid than a 40°F day with 100% humidity because the dew point is higher.
What is the highest dew point ever recorded?
The highest dew point ever recorded was 35°C (95°F) on July 8, 2003 in Dhahran, Saudi Arabia, with an air temperature of 42°C (108°F) and relative humidity of 68.5%. Such extreme dew points are extremely dangerous as they prevent the body from cooling through sweat evaporation, leading to heat stroke risk.
How does dew point affect human comfort?
Dew point directly affects how comfortable humans feel because it determines how effectively sweat can evaporate from the skin. High dew point means the air is already saturated with moisture, slowing evaporation and making us feel hot and sticky. Low dew point allows rapid evaporation, making us feel cooler. This is why the same temperature can feel very different in humid vs dry climates.
What is the frost point?
When the dew point is below 0°C (32°F), water vapor condenses directly as frost (ice crystals) instead of liquid dew. The frost point is the temperature at which this occurs, calculated using different Magnus coefficients for ice surfaces. The frost point is typically slightly colder than the corresponding dew point for the same air temperature and relative humidity.
What are practical applications of dew point?
Dew point measurement is used in: 1) Meteorology for weather forecasting and fog prediction, 2) Aviation to assess icing risk on aircraft wings and carburetors, 3) Agriculture to manage greenhouse humidity and prevent crop diseases, 4) HVAC system design for comfortable indoor environments, 5) Industrial processes like compressed air drying and gas processing, 6) Electronics manufacturing to prevent condensation on sensitive components.