How dew point calculator works
The dew point is the temperature at which air, cooled at constant pressure, becomes saturated and water vapour starts to condense. Warm air holds more vapour than cold air, so the same relative humidity means a higher dew point on a hot day than a cold one. The calculator uses the Magnus form of the Clausius–Clapeyron relation with the Alduchov & Eskridge (1996) constants: gamma = ln(RH/100) + 17.625·T / (243.04 + T), then dew point = 243.04·gamma / (17.625 − gamma), all in °C.
The tool takes your air temperature (°C or °F, converted internally) and relative humidity in percent, computes the dew point in °C, and reports it in both °C and °F. It also shows the spread — air temperature minus dew point — which is how meteorologists gauge how close the atmosphere is to saturation: fog and dew become likely when the spread shrinks to a couple of degrees, while a wide spread signals dry air.
Finally, the dew point is placed on the comfort scale meteorologists quote for how muggy air feels: below 55 °F is dry, 55–60 °F comfortable, 60–65 °F slightly humid, 65–70 °F humid, 70–75 °F oppressive and above 75 °F miserable. Dew point — not relative humidity — is the honest measure of mugginess because it tracks the actual moisture in the air. All math runs in your browser.