Dew Point Calculator
The dew point is the temperature at which air becomes saturated and water vapor begins to condense. Unlike relative humidity, the dew point gives you an absolute measure of moisture in the air. A dew point of 65°F (18°C) feels sticky regardless of the actual temperature, while anything below 50°F (10°C) feels dry and pleasant.
This calculator uses the Magnus formula (Alduchov and Eskridge, 1996):
Td = (b * alpha) / (a - alpha)
Where alpha = (a * T) / (b + T) + ln(RH/100), with constants a = 17.27 and b = 237.7°C.
**Dew point comfort scale:** - **Below 50°F (10°C):** Dry and pleasant - **50-55°F (10-13°C):** Comfortable - **55-60°F (13-16°C):** Slightly humid - **60-65°F (16-18°C):** Getting sticky - **65-70°F (18-21°C):** Uncomfortable for many - **70-75°F (21-24°C):** Oppressive - **Above 75°F (24°C):** DangerousFor example, on a 90°F day at 40% relative humidity, the dew point is about 63°F, which is the edge of sticky. On the same 90°F day at 70% humidity, the dew point jumps to 79°F, which is dangerously oppressive.
Pilots use the temperature-dew point spread to predict fog and cloud bases. When the spread narrows to about 2-3°C, fog formation becomes likely. The cloud base height in feet is roughly 400 times the spread in °F.