Dew Point Calculator

Created by Luis Fernando
Based on research by
Mark G. Lawrence The Relationship between Relative Humidity and the Dewpoint Temperature in Moist Air: A Simple Conversion and Applications Bulletin of the American Meteorological Society 86(2) (01 Feb 2005)
Last updated: Jul 28, 2022

Welcome to the dew point calculator, a tool that will let you know what is the dew point (also known as dewpoint) in the environment, given the temperature and relative humidity. The dewpoint is one of the most relevant properties in thermodynamics, present in many applications, such as:

  • Cloud base: Have you ever wondered what is the temperature of clouds? To know it, you need our cloud base calculator, and calculating the dew point is necessary before using it.
  • Air density: The air composing our atmosphere doesn't have a constant density, and at very high altitudes, it can reach ridiculously low values. To discover how low it can be, you need the dew point and our air density calculator. Another way of expressing air density is through something known as density altitude, mainly used in the aviation industry.
  • Heat index: Maybe it's happened that you checked the temperature provided by your weather app, and it's too low compared to the heat sensation you feel. In that situation, we can say the apparent temperature differs significantly from the real one because the heat index is higher than usual. To know how high, use our heat index calculator.

What is the dew point?

The dew point is the temperature at which the water vapor in the air reaches its saturation state. The water vapor will condense and form liquid water — dew — when we cool the air down to this temperature at constant pressure.

As we can see in the following chart, the dew point increases linearly with the temperature at constant relative humidity.

Dew point chart
Dew point chart. Easchiff, CC BY-SA 4.0, via Wikimedia Commons.

How do I calculate the dew point?

There are various ways to approximate the dew point. Our dew point calculator uses the following equation:

  • Tdp = bα/(a - α)
  • α = ln(RH%/100) + aT/(b + T)

where:

  • Tdp — Dewpoint;
  • T — Air temperature;
  • RH — Relative humidity of the air, expressed as a percentage (e.g., 50%);
  • a and b — The Magnus coefficients.

The coefficient values recommended by Alduchov and Eskridge are:

  • a = 17.625; and
  • b = 243.12°C.

And that's the formula. Hopefully, now you know how to calculate the dew point, even without the calculator. To continue your learning journey, you can look at the calculators mentioned at the beginning of the article.

Luis Fernando
Temperature
°F
Relative humidity
%
Dew point
°F
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