Dew Point Calculator: Humidity & Comfort Scale

Select your calculation mode at the top: “Calculate For: Dew Point” when you know air temperature and relative humidity, or “Calculate For: Relative Humidity” when you know air temperature and dew point. Enter temperatures in Fahrenheit or Celsius—both fields stay synchronized, so type in whichever unit you prefer and the other updates automatically. For dew-point mode, input the current air temperature and the relative humidity as a percentage between 0 and 100. For humidity mode, provide the air temperature and the observed dew point. The result appears instantly alongside a color-coded comfort badge: green for dry conditions (dew point below 50°F), yellow for comfortable, orange for muggy, and red for oppressive humidity above 70°F. Toggle between °F and °C to switch your primary display unit without re-entering data.

Dew point is the temperature at which air becomes saturated with moisture and condensation begins. It's useful for weather forecasting, HVAC sizing, and knowing when to expect fog or condensation. Unlike relative humidity, which depends on temperature, dew point is a direct measure of moisture: higher dew point means more water vapor in the air, and a muggier feel.

The calculator uses the Magnus-Tetens approximation. First $\gamma(T, RH) = \ln(RH/100) + \frac{bT}{c+T}$ where T is air temperature (°C) and RH is relative humidity (0–100). Then $T_d = \frac{c\gamma}{b - \gamma}$ gives the dew point in °C. Constants: b = 17.625, c = 243.04. To find RH from T and dew point $T_d$, use $\gamma = \frac{bT_d}{c+T_d}$ and $RH = 100 \cdot e^{\gamma - \frac{bT}{c+T}}$.