Dew Point Calculator
The dew point is the temperature the air must cool to before its water vapour starts to condense, as dew, fog or droplets on a cold glass. When the dew point and the air temperature are close, the air is nearly saturated.
This page finds the dew point from the air temperature and the relative humidity.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
This page uses the Magnus formula, a standard approximation. It combines the air temperature and the humidity into one intermediate value, then converts that value back into a temperature.
The approximation is close across ordinary air temperatures, usually within about half a degree. Very cold or very hot conditions are less precise.
Worked example
Air at 77 °F with 60% relative humidity has a dew point of 62.048 °F.
Questions
Why is the dew point lower than the air temperature?
Unless the air is fully saturated, it can hold more water vapour than it has, so it must cool before condensation starts. The drier the air, the bigger the gap.
Does a higher dew point mean rain is coming?
Not by itself. The dew point shows how much moisture the air holds, but rain also needs lift and cooling.
Is the dew point the same at every height?
No. Temperature and humidity change with height, so the dew point at one spot can differ from the reading at ground level.
More like this
- Wet Bulb CalculatorWet bulb temperature from air temperature and humidity.
- Impulse CalculatorImpulse from force and time, or mass and speed change.
- Earth Curvature CalculatorHow far the ground drops away over a distance.
- Viscosity CalculatorKinematic viscosity from dynamic viscosity and density.
- PCB Trace Width CalculatorTrace width for a current and a temperature rise.
- Lever Mechanical Advantage CalculatorEffort needed to move a load with a lever.