Dew Point Calculator
Find the dew point from the temperature and relative humidity – or the humidity from the dew point – with the absolute humidity and how muggy the air feels.
What the dew point tells you
The dew point is the temperature to which air must cool for its water vapor to condense. It measures how much moisture is actually in the air, regardless of the temperature – which is why forecasters use it to describe how humid a day feels. Relative humidity, by contrast, changes all day as the air warms and cools.
Worked example
At 72 °F and 60% relative humidity the dew point is 57.4 °F. Any surface colder than that – a glass of iced tea, a cold window, an uninsulated pipe – will collect condensation. The air holds about 11.8 g of water per cubic meter.
How humid does it feel?
| Dew point | Feels |
|---|---|
| below 50 °F | dry |
| 50–55 °F | very comfortable |
| 55–61 °F | comfortable |
| 61–65 °F | slightly humid |
| 65–70 °F | humid, sticky |
| 70–75 °F | muggy, oppressive |
| 75 °F and above | very oppressive |
The formula
The calculator uses the Magnus formula with the coefficients a = 17.625 and b = 243.04 °C, accurate to about 0.4 °F for normal weather. Switch to Dew point to enter a dew point and get the relative humidity instead.
Mold and condensation at home
Indoors, keep the dew point well below the temperature of your coldest surfaces. If walls or window frames are colder than the dew point, moisture condenses and mold can grow. Keeping indoor humidity between 30% and 50% usually prevents this in winter.
Frequently asked questions
What is a comfortable dew point?
Between about 50 and 60 °F. Above 65 °F most people find the air sticky.
What is the dew point at 70 °F and 40% humidity?
About 44.6 °F.
Can the dew point be higher than the temperature?
No. When the air cools to its dew point, the relative humidity is 100% and water condenses.