Dew Point Calculator
Relative humidity is the most misleading number in the weather app: 70% humidity at 15°C is a crisp autumn day, while 70% at 30°C is a swamp - the same percentage, completely different air. The dew point cuts through it by stating the actual water vapor content: the temperature at which that air would saturate. Meteorologists read comfort straight off it, and this calculator runs the Magnus formula the moment you type.
The comfort bands under the result are the ones forecasters actually use - below 10°C dry, 10-16 comfortable, 16-21 noticeable, 21-24 muggy, and past 24 oppressive - plus a stat most tools skip: the temp-dew-point spread, which tells you how close fog or overnight dew is. Your last inputs are remembered, the result lands in the tab title, and the share link carries the whole reading.
How to use
- Pick °C or °F, then enter air temperature and relative humidity.
- Read the dew point and its comfort verdict instantly.
- Watch the temp-dew-point spread - when it nears zero, fog and dew are close.
Frequently asked questions
Why is dew point better than relative humidity?
Relative humidity is water vapor relative to what the air could hold at its current temperature - so it changes with temperature even when the moisture doesn't. Dew point measures the moisture itself: a 20°C dew point means the same sticky air in Dallas or Delhi. That's why pilots and meteorologists track dew point, not RH.
What dew point feels muggy?
Most people: below 10°C dry, 10-16 comfortable, 16-21 noticeable, 21-24 muggy, 24+ oppressive. Past about 26-28°C even resting in shade is miserable, because sweat stops evaporating efficiently once the dew point nears skin temperature - evaporation is the only cooling your body has.
How is dew point calculated?
The Magnus approximation, the same one in most weather station firmware: dew point = 243.12·γ ÷ (17.62 − γ), where γ = ln(RH/100) + 17.62·T ÷ (243.12 + T). Accurate to a fraction of a degree across normal weather; the calculator also converts the result to absolute humidity in g/m³.
What does it mean when dew point equals air temperature?
The air is saturated - 100% relative humidity - and any further cooling forces water out: dew on grass, fog in the air, clouds in the sky. The 'spread' stat shows how close you are; pilots use the same spread to predict morning fog at their destination.