Dew Point Calculator - Free Online Calculator

Dew point is the absolute measure of moisture in the air - unlike relative humidity which depends on temperature. A 50% RH reading at 30°C means the air holds lots of water (about 13g/kg); the same 50% RH at 5°C holds much less (about 3g/kg). Dew point cuts through this confusion: it tells you the temperature at which air becomes saturated (100% RH) and dew/condensation forms. A dew point of 22°C means the air carries enough moisture that any surface cooler than 22°C will get wet. This is why your cold drink glass 'sweats' on a Mumbai July day - the glass surface (chilled by the drink) drops below the air's dew point.

For Indian users, dew point directly explains the 'feels-like' summer/monsoon discomfort. Coastal cities like Mumbai, Chennai, Kochi have summer dew points often above 25°C - oppressive territory where sweat doesn't evaporate. Delhi and inland North India have lower dew points (15-20°C in summer) - hotter air but drier, which feels less sticky despite being warmer. Bangalore at moderate elevation has comfortable dew points (typically 17-21°C). This calculator uses the Magnus formula, accurate to within 0.4°C across normal weather conditions, and gives both °C and °F output.

Magnus formula (also called August-Roche-Magnus): α = (a·T)/(b + T) + ln(RH/100), where a = 17.27 and b = 237.7°C are empirical constants. Dew point Td = (b·α) / (a − α). Derived from the Clausius-Clapeyron relation describing how saturation vapour pressure changes with temperature. The constants are fitted to match measured vapour pressure data.

Why dew point > air temperature is impossible: 100% RH means dew point equals air temperature. Higher dew point than air temperature would imply RH > 100%, which is the supersaturated unstable state that immediately condenses. So dew point is always ≤ air temperature, equal only at fog/dew formation conditions.

Comfort interpretation: dew point below 10°C - dry, comfortable. 10-15°C - comfortable. 15-18°C - somewhat humid but tolerable. 18-21°C - sticky, noticeable discomfort. 21-24°C - oppressive, very humid. Above 24°C - extremely uncomfortable, hard to function outdoors. Indian coastal monsoon dew points routinely exceed 24°C. Air-conditioned spaces typically maintain 15-18°C dew points; reducing room dew point is one reason AC feels so much better than just fans (fans don't reduce humidity).