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Dew Point Calculator

Find the dew point from air temperature and relative humidity, in °F and °C, with a comfort rating.

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Uses the Magnus formula, which is accurate to within a few tenths of a degree for normal weather. Comfort ratings are a general guide.

Quick Answer

The dew point is the temperature the air must cool to before water vapor condenses into dew. At 85°F and 60% relative humidity, the dew point is about 69.6°F, which feels humid and uncomfortable. Dew points above about 65°F usually feel humid to most people.

Last updated: 2 November 2026 ·How we calculate this: the Magnus formula

Table of Contents

How This Dew Point Calculator Works

Enter the air temperature and relative humidity. The calculator uses the Magnus formula to find the dew point, shows it in both °F and °C, and gives a simple comfort rating.

Quick explanation: the closer the dew point is to the air temperature, the more humid the air.

  • Dew point: an absolute measure of moisture in the air.
  • Relative humidity: how full of moisture the air is at its current temperature.
  • 100% humidity: the dew point equals the air temperature.

How to Use the Dew Point Calculator

  1. Choose Fahrenheit or Celsius.
  2. Enter the air temperature.
  3. Enter the relative humidity in percent.
  4. Press Calculate.
  5. Read the dew point, the comfort rating and the gap between air temperature and dew point.

Core Formulas

  • Step 1: γ = ln(RH ÷ 100) + (b × T) ÷ (c + T)
  • Step 2: dew point = (c × γ) ÷ (b − γ)
  • Constants: b = 17.62 and c = 243.12°C

T is the air temperature in °C and RH is relative humidity in percent.

Key Terms

  • Dew point: the temperature at which air becomes saturated and water starts to condense.
  • Relative humidity: the amount of moisture in the air compared with the most it can hold at that temperature.
  • Condensation: water vapor turning into liquid on a cooler surface.
  • Saturation: the point at which air holds as much water vapor as it can.

Worked Example

The air is 25°C with 50% relative humidity.

  • γ = ln(0.5) + (17.62 × 25) ÷ (243.12 + 25) = 0.9498
  • Dew point = (243.12 × 0.9498) ÷ (17.62 − 0.9498)
  • Dew point = 13.9°C (56.9°F)

Real-Life Examples

  • Planning a run: at 75°F and 80% humidity, the dew point is about 68°F, so it will feel muggy and sweat will not dry easily.
  • Painting outside: many paint makers advise that surfaces should stay a few degrees above the dew point so moisture does not form.
  • Condensation at home: at 70°F and 50% indoor humidity, the dew point is about 50°F, so windows colder than that will fog.
  • Morning dew or frost: if the night temperature drops below the dew point, dew forms. Below freezing, it can become frost.

Dew Point vs Relative Humidity

  • Relative humidity: depends on temperature, so it rises at night even when the moisture stays the same.
  • Dew point: shows the actual amount of moisture, so it is a better guide to how muggy it feels.
  • Example: 50°F with 90% humidity feels fine, while 90°F with 50% humidity feels very humid, because its dew point is far higher.

Dew Point Comfort Guide

A common guide used in weather forecasts. People differ in what feels comfortable.

Dew pointHow it feels
Below 55°F (13°C)Dry and comfortable
55 to 60°FComfortable
60 to 65°FGetting sticky
65 to 70°FHumid and uncomfortable
70 to 75°FVery humid, oppressive
Above 75°F (24°C)Extremely humid

Common Mistakes to Avoid

  • Judging comfort by humidity alone. Use the dew point for a clearer picture.
  • Mixing units. Make sure the temperature unit matches the setting.
  • Entering humidity as a decimal. Enter 60, not 0.60.
  • Ignoring surface temperature. Cold surfaces can reach the dew point before the air does.
  • Expecting dew point to change with heating. Warming air lowers relative humidity, but the dew point stays the same.

Frequently Asked Questions

Most people find dew points below about 60°F comfortable and above 65°F humid.

No. At most it equals the air temperature, when relative humidity is 100%.

It shows how much moisture is in the air, which is a better guide to how sticky it feels than relative humidity.

Fog often forms when the air temperature falls to the dew point, so the two are equal or very close.

Not by itself, but humid air provides the moisture that storms need.

Dew points in the mid-70s °F and higher, combined with heat, can make it hard for the body to cool itself.

Use a dehumidifier or air conditioning, which remove moisture. Venting kitchens and bathrooms also helps.

Many guides suggest keeping indoor relative humidity between about 30% and 50% to limit mold and dust mites.

It is the same physical temperature, just shown in a different unit. This calculator shows both.

Yes. A high dew point slows sweat evaporation, so heat feels worse. Our heat index tool combines both.

The glass is colder than the dew point of the air around it, so water vapor condenses on its surface.

When the dew point is below freezing, it is called the frost point, as water vapor turns straight into ice.

References & Sources

SourceUsed ForLink
National Weather Service, Dew point vs humidity How dew point relates to comfort. https://www.weather.gov/arx/why_dewpoint_vs_humidity
Wikipedia, Dew point The Magnus formula and constants. https://en.wikipedia.org/wiki/Dew_point