Dew Point Calculator

Find the dew point — the temperature at which air becomes saturated and dew forms — from temperature and relative humidity, in °F or °C, with a comfort rating. Calculates in your browser.

Dew point

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Comfort-

Show the math

The Magnus-Tetens approximation relates dew point to temperature and humidity:

Td = c·γ ÷ (b − γ), γ = ln(RH/100) + bT ÷ (c + T)

With b = 17.625 and c = 243.04 °C, this is accurate to a few tenths of a degree in normal weather. The dew point can never exceed the air temperature, when they meet, the air is saturated and fog or dew forms. All math runs locally in your browser.

What this does

A dew point calculator finds the temperature at which air would become saturated and dew, fog, or condensation forms, from the current temperature and relative humidity. Unlike humidity, the dew point is an absolute measure of how much moisture the air holds — the higher it is, the muggier it feels.

How to use it

  1. Choose Fahrenheit or Celsius.
  2. Enter the air temperature.
  3. Enter the relative humidity.
  4. Read the dew point and its comfort rating.

How it works

The Magnus-Tetens approximation uses the constants b = 17.625 and c = 243.04°C. It is accurate to within a few tenths of a degree over normal weather conditions. Celsius is used internally and Fahrenheit inputs are converted.

Td = c·γ ÷ (b − γ), γ = ln(RH/100) + bT/(c+T)

Understanding your result

A dew point below 50°F feels dry and comfortable; 60°F starts to feel sticky; above 70°F is oppressive and sweat no longer evaporates well. The dew point can never exceed the air temperature — when they are equal the air is fully saturated (100% humidity) and fog or dew forms.

Example

At 68°F (20°C) with 50% humidity, the dew point is about 49°F (9°C) — comfortable.

Sources & methodology

Last updated .

Frequently asked questions

What is the difference between dew point and humidity?

Relative humidity is a percentage that depends on temperature, while the dew point is an absolute temperature. A dew point of 70°F always feels muggy, whereas “70% humidity” feels very different at 50°F than at 90°F.

Can the dew point be higher than the temperature?

No. The dew point is always at or below the air temperature. When they meet, the air is saturated and dew, fog, or condensation forms.

Is my data stored?

No. Everything is calculated locally in your browser.