Dew Point Calculator

Relative humidity (RH) is expressed as a percentage and tells you how close the air is to saturation at the current temperature. Dew point is an actual temperature — the point at which condensation forms. As temperature rises throughout the day, RH drops even though the actual moisture content stays the same. Dew point remains constant as long as no moisture is added or removed, making it more reliable for expressing comfort.

When dew point is high, the air is already holding a lot of water vapor. Your body cools itself primarily through sweat evaporation — but if the air is already nearly saturated with moisture, sweat can't evaporate efficiently. Heat builds up in your body faster than it can be released. This is why a 32°C Mumbai day with a 25°C dew point (typical monsoon) feels significantly more dangerous than a 42°C Jaisalmer day with a 10°C dew point (dry desert).

After sunset, surfaces like grass, car hoods, and leaves radiate heat and cool below the air temperature. When a surface cools to the dew point temperature, water vapor in the air adjacent to that surface condenses into liquid water droplets — dew. On clear nights (no cloud insulation), surfaces can cool rapidly, explaining why dew is most common after clear nights. On foggy mornings, the air itself has cooled to its dew point.

Indoor comfort guidelines suggest maintaining 30–50% relative humidity at typical indoor temperatures (20–22°C). At 22°C and 45% RH, the dew point is about 9°C — comfortable. At 22°C and 70% RH, the dew point is about 16°C — noticeably humid. Condensation on AC vents or windows occurs when the surface cools below the indoor dew point. Keeping indoor dew point below 13°C prevents most condensation problems.

For outdoor physical activity, a dew point above 18°C (65°F) begins to impair cooling. Above 21°C (70°F), heavy exertion is risky for even fit people — this is typical of Mumbai, Chennai and Kolkata during peak monsoon. Above 24°C (75°F), prolonged outdoor exertion can be life-threatening. The highest dew points ever recorded are around 35°C (95°F) in the Persian Gulf — conditions so extreme that they exceed the human body's ability to maintain core temperature even at rest.