Free dew point calculator. Find the condensation temperature based on humidity and air temperature. Magnus formula, comfort chart, and practical examples.
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Calculate dew point instantly with our free calculator. Enter temperature and relative humidity to find the condensation temperature. Ideal for HVAC, compressed air systems, astronomy, agriculture, and building moisture control.
Dew point is the temperature at which air must cool for water vapor to condense into dew or fog. It's calculated using the Magnus formula from ambient temperature and relative humidity. Unlike relative humidity (which changes with temperature), dew point directly indicates how much moisture is in the air.
Magnus Formula
Td = (c × γ) / (b - γ), where γ = ln(RH/100) + (bT)/(c+T)Dew point is the best indicator of how humid and uncomfortable the air feels.
When temperature approaches dew point, fog, dew, or precipitation may form.
Prevent condensation, mold, and moisture damage in buildings.
Controlling dew point in pneumatic systems prevents corrosion, freezing, and damage to valves and cylinders.
Astronomers calculate dew point to prevent condensation on lenses and mirrors during nighttime observations.
Monitoring dew point helps prevent fungal diseases and plan irrigation efficiently.
Designing systems that keep surfaces above dew point prevents mold and structural damage.
Predicting fog formation, carburetor icing, and visibility conditions for safe flights.
Applying paint when the surface is at least 3°C above dew point ensures proper adhesion.
Dew point is calculated using the Magnus formula: Td = (c × γ) / (b - γ), where γ = ln(RH/100) + (b×T)/(c+T). The constants are b=17.67 and c=243.5°C. For example, at 25°C with 60% humidity, the dew point is approximately 16.7°C.
A 'normal' or comfortable dew point is between 10-15°C (50-59°F). Below 10°C the air feels dry. Between 15-18°C is pleasant. Between 18-21°C feels humid. Above 21°C is uncomfortable and oppressive.
70% is relative humidity, not dew point. At 25°C with 70% humidity, the dew point is ~19°C, which is considered humid and uncomfortable. To convert humidity to dew point, you also need to know the ambient temperature.
In industrial compressed air systems, typical dew points vary: Class 1 (-70°C), Class 2 (-40°C), Class 3 (-20°C), Class 4 (+3°C). A low dew point prevents condensation and corrosion in pipes and pneumatic equipment.
A dew point of 13°C (55°F) or below feels comfortable and dry. Between 13-18°C feels increasingly humid. Above 18°C (65°F) feels very humid, and above 21°C (70°F) is oppressive and impairs sweating.
Relative humidity is a percentage that changes with temperature (the same air can have 50% in the morning and 80% at night). Dew point is a fixed temperature that directly indicates how much water is in the air. That's why meteorologists prefer dew point.
No, dew point can never exceed ambient temperature. When they're equal (100% humidity), the air is saturated and fog, dew, or condensation forms. If the calculated dew point were higher, it means an error in the input data.
Astronomers calculate dew point to protect telescopes and optical equipment. If equipment temperature drops below the dew point, condensation forms on lenses and mirrors, ruining observations. That's why they use dew heaters.