About the Dew Point Calculator
The dew point is the temperature to which air must cool for water vapour to start condensing into dew, fog or cloud. It is a direct measure of how much moisture is in the air, and a better guide to how humid it feels than relative humidity. Enter the air temperature and relative humidity in Celsius or Fahrenheit, and this calculator uses the Magnus formula to find the dew point, shows it in both scales and rates the comfort level from dry to oppressive. It runs entirely in your browser.
Updated October 2026
How to use the Dew Point Calculator
- 1Choose Celsius or Fahrenheit.
- 2Enter the air temperature.
- 3Enter the relative humidity as a percentage above 0 and up to 100.
- 4Read the dew point and the comfort rating.
- 5Press Copy result to save the numbers.
Comfort by dew point
- Below 50 °F (10 °C): dry and comfortable
- 50 to 59 °F (10 to 15 °C): comfortable
- 60 to 64 °F (16 to 18 °C): a little sticky
- 65 to 69 °F (18 to 21 °C): humid
- 70 °F (21 °C) and above: very humid to oppressive
Using dew point around the house
In winter, warm indoor air meets cold windows. If the glass is colder than the room's dew point, condensation forms. Lowering indoor humidity, ventilating bathrooms and kitchens and using extractor fans reduce the dew point. In summer, a high dew point inside explains why a room feels clammy even when the thermostat is on, and why air conditioners remove moisture as well as heat.
In weather and gardening
Growers watch the gap between the night's expected low temperature and the dew point, because frost and heavy dew are likely when they are close. Pilots and drivers watch for fog, which forms as the air cools to the dew point. The tool is accurate for everyday conditions; it is not intended for scientific measurements at extreme temperatures or altitudes.
Related tools
The Heat Index Calculator combines temperature and humidity into a feels-like value for hot weather, and the Wind Chill Calculator does the same for cold wind. The Temperature Converter changes the scale, the Unit Converter handles other measurements, and the Online Clock shows the time of day when you plan for dawn dew.
Features
- Dew point from temperature and relative humidity
- Magnus formula, accurate for everyday weather
- Celsius and Fahrenheit together
- Comfort rating from dry to oppressive
- Gap between air temperature and dew point
- Checks for impossible humidity
- Runs in your browser
Frequently asked questions
What is the dew point?
It is the temperature at which air becomes saturated and water vapour starts to condense. If a surface or the air itself cools to the dew point, dew forms on the ground, fog forms in the air, or moisture appears on a cold glass.
How do I calculate the dew point?
A common approximation is the Magnus formula, which uses the air temperature and relative humidity. A temperature of 25 °C at 60 percent humidity gives a dew point of about 16.7 °C. The calculator applies the formula and shows the result in both scales.
What dew point is comfortable?
Most people feel comfortable when the dew point is below about 60 °F (16 °C). Between 60 and 65 °F it starts to feel sticky, between 65 and 70 °F it feels humid, and above 70 °F (21 °C) it feels oppressive. The calculator shows the band for your result.
Is dew point better than relative humidity?
For judging comfort, yes. Relative humidity depends on the temperature, so the same moisture level gives a high percentage on a cool morning and a low one on a hot afternoon. The dew point stays the same, so it is a steadier measure of how muggy the air is.
What does it mean when the dew point equals the air temperature?
The relative humidity is 100 percent. The air is saturated, and fog, mist or dew form. The smaller the gap between the two numbers, the closer the air is to saturation.
Why does dew point matter for homes?
If a window, wall or cold pipe is below the dew point of the room air, condensation forms on it, which can lead to damp and mould. Knowing the dew point helps you decide when to ventilate or use a dehumidifier.