Dew Point & Humidity Calculator
Calculate dew point, wet-bulb temperature, heat index, vapor pressure, absolute humidity, mixing ratio, specific humidity and moist-air density from temperature and relative humidity.
Input
Dry-bulb (ambient) temperature, in the unit selected above.
Optional. Standard sea-level pressure is 1013.25 hPa. Needed for mixing ratio, specific humidity and air density.
Output
| Metric | Value |
|---|---|
| No data yet | |
Guides
The Dew Point & Humidity Calculator turns two everyday weather readings — air temperature and relative humidity — into a full set of psychrometric values. From a single measurement it derives the dew point, wet-bulb temperature, heat index, saturation and actual vapor pressures, absolute humidity, and (when you supply air pressure) the mixing ratio, specific humidity and moist-air density. It also classifies the result into a plain-language comfort band, so you know at a glance whether the air will feel crisp, sticky or oppressive.
How to use it
- Choose your temperature unit — Celsius or Fahrenheit.
- Enter the air temperature (the ordinary dry-bulb reading from a thermometer).
- Enter the relative humidity as a percentage from 0 to 100.
- Optionally enter the air pressure in hectopascals (hPa). Standard sea-level pressure is 1013.25 hPa. Leave it blank if you only need dew point, wet-bulb and humidity figures.
Results update instantly as you type. Temperatures in the results table are shown in the same unit you selected for the input.
What the numbers mean
- Dew point — the temperature to which air must cool for water to start condensing. It is the single best indicator of how "muggy" the air feels, because it does not change as the air warms during the day.
- Wet-bulb temperature — the lowest temperature reachable by evaporative cooling; important for heat-stress and industrial cooling.
- Heat index — the apparent "feels-like" temperature combining heat and humidity. It is only physically meaningful above about 27 °C (80 °F); below that the calculator flags it as not applicable.
- Absolute humidity — the actual mass of water vapor per cubic metre of air (g/m³).
- Mixing ratio / specific humidity — grams of water vapor per kilogram of dry or moist air; these require air pressure.
The formulas
Dew point and vapor pressure use the Magnus-Tetens approximation with the Alduchov & Eskridge (1996) coefficients, accurate to better than 0.4% between −40 °C and +50 °C. Wet-bulb temperature uses Stull's (2011) single-equation approximation, and the heat index uses the NOAA Rothfusz regression. Absolute humidity and air density come from the ideal gas law.
FAQ
What is a comfortable dew point? As a rule of thumb, a dew point at or below 10 °C feels dry, up to 16 °C feels comfortable, 16–18 °C starts to feel sticky, 18–21 °C is noticeably humid, and above 24 °C is oppressive.
Do I have to enter air pressure? No. Dew point, wet-bulb temperature, heat index and absolute humidity are computed without it. Pressure is only needed for mixing ratio, specific humidity and moist-air density.
Why does the heat index sometimes say "n/a"? The Rothfusz regression is only valid in hot conditions. Below roughly 80 °F (27 °C) the calculator shows the fallback estimate but marks it as not applicable, since "feels-like" heat has little meaning in cool air.
Can I convert between Celsius and Fahrenheit? Yes — pick your unit before entering the temperature, and every temperature-based result is reported back in that same unit.
Privacy
This calculator runs entirely in your browser. Your temperature, humidity and pressure values are never uploaded or stored — the math happens locally on your device.