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Dew Point Calculator

This dew point calculator estimates dew point from ambient temperature and relative humidity using a common Magnus-Tetens approximation. Toggle °F/°C. Useful for comfort checks and condensation risk — not a substitute for calibrated instruments.

Ambient air temperature. Switching units converts this number.

Greater than 0 and at most 100. 100% means the air is saturated.

Temperature unit

Dew point

Dew point
55.46°F
Comfort
Slightly humid
Dew point (°C)
13.04°C
Dew point (°F)
55.46°F
Air temperature
70°F
Relative humidity
60%
  1. 70°F = (70 − 32) × 5/9 = 21.1111°C.
  2. γ = ln(60/100) + (17.27 × T) / (237.7 + T) = 0.8979, with T in °C.
  3. Dew point = (237.7 × γ) / (17.27 − γ) = 13.04°C (55.46°F).

Magnus-Tetens is an everyday estimate for comfort and condensation checks. It is not a substitute for a calibrated sensor. The math stays in your browser.

How to use

  1. Enter the air temperature and choose °F or °C. Switching units converts the temperature you already typed.
  2. Enter relative humidity as a percent greater than 0 and at most 100.
  3. Read the dew point in the unit you selected. The formula runs in Celsius, then converts back.
  4. Use the comfort label as a rough guide. A higher dew point means the air holds more moisture.

Formula

Magnus-Tetens uses air temperature T in °C and relative humidity RH as a percent. γ = ln(RH/100) + (17.27 × T) / (237.7 + T). Dew point in °C = (237.7 × γ) / (17.27 − γ). Fahrenheit is converted with °C = (°F − 32) × 5/9 before that formula, then back with °F = °C × 9/5 + 32. At 100% humidity the dew point equals the air temperature. The approximation is for about −40°C to 60°C.

Example. At 70°F and 60% relative humidity, 70°F converts to 21.11°C. Magnus-Tetens gives a dew point of 13.04°C, which is 55.46°F.

Example. At 20°C and 50% relative humidity, the dew point is 9.25°C. At 100% relative humidity the dew point equals the air temperature.

Frequently asked questions

What is dew point?

The temperature at which air becomes saturated and water vapor begins to condense.

How is dew point calculated?

From temperature and relative humidity using an approximation such as Magnus-Tetens.

Is a higher dew point more humid?

Yes. Higher dew points feel muggier because more moisture is in the air.

Can I use Fahrenheit?

Yes. Switch units; the tool converts internally for the formula.

Is this exact enough for labs?

It is an estimate for everyday use. Labs should use calibrated sensors.

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