Calculate the dew point from air temperature and humidity, or the humidity from a known dew point.
The dew point is the temperature at which air becomes saturated and dew or fog forms. Air at 25 °C with 60% humidity has a dew point of 16.7 °C — comfortable. A dew point above about 21 °C (70 °F) feels oppressive.
The dew point is the temperature to which air must be cooled for water vapour to condense. It is a direct measure of how much moisture is in the air, and a better guide to comfort than relative humidity, which changes with temperature. This calculator finds the dew point from air temperature and relative humidity, and a second tool finds relative humidity from air temperature and dew point.
It is useful for weather watching, preventing condensation and mould in buildings, gardening (frost and dew), and judging how humid it feels. See also the Heat Index Calculator.
The calculator uses the Magnus approximation, accurate to a fraction of a degree for normal weather.
| Air temperature | Humidity | Dew point | Comfort |
|---|---|---|---|
| 25 °C | 60% | 16.7 °C · 62.1 °F | Sticky — humid |
| 30 °C | 50% | 18.4 °C · 65.2 °F | Muggy and uncomfortable |
| 35 °C | 70% | 28.7 °C · 83.7 °F | Miserable — extremely humid |
| 20 °C | 40% | 6 °C · 42.8 °F | Dry |
| 77 °F | 60% | 16.7 °C · 62.1 °F | Sticky — humid |
| Dew point (°F) | Dew point (°C) | How it feels |
|---|---|---|
| Below 50 | Below 10 | Dry |
| 50–55 | 10–13 | Pleasant and dry |
| 55–60 | 13–16 | Comfortable |
| 60–65 | 16–18 | Sticky — humid |
| 65–70 | 18–21 | Muggy and uncomfortable |
| 70–75 | 21–24 | Oppressive |
| 75 and above | 24 and above | Miserable — extremely humid |
When a surface — a cold glass, a window pane or a wall — is colder than the dew point of the air around it, moisture condenses on it. Keeping indoor surfaces warmer than the indoor dew point (with ventilation and dehumidification) prevents condensation and mould.
The temperature at which air is saturated with water vapour and begins to condense into dew, fog or cloud.
Use the Magnus formula with the air temperature and relative humidity — this calculator does it for you.
Below about 16 °C (60 °F) most people feel comfortable; above 21 °C (70 °F) it feels oppressive.
Yes, because dew point measures the actual amount of moisture, while relative humidity depends on the temperature.
No. At most it equals the air temperature, which happens at 100% humidity.
Water vapour condenses, forming dew on surfaces, fog in the air, or frost if below freezing.
Use the second calculator with the air temperature and dew point.
The Magnus formula is accurate to about ±0.4 °C for typical weather between −45 °C and 60 °C.
Yes — choose °F and the results are shown in both scales.
No. Everything runs in your browser.
