Dew Point

What Is Dew Point and How to Calculate It

Everyone has probably heard the term “dew point” talked about, especially on weather channels. However, it’s essential to know what it is. Once you’ve done that, you want to figure out how to calculate it so that you know how it can affect you.

The information you’re going to get today is highly valuable. It contains everything you need to know, so you should continue reading it to get the most from it.

Your friends probably need to know about dew point, too. Once you’ve finished reading it for yourself, share it so that your friends can learn how to measure it correctly.

Dew Point Definition

According to the NWS (National Weather Service), the dew point is just the temperature that air should be cooled to reach saturation. When there is a higher dew point, there is more moisture in the air.

Dew Point Characteristics

Dew point temperature can tell you how comfortable it’s going to be outside. When the dew point is higher, it’s harder for the sweat to evaporate from the skin. That means it is going to feel muggy and hot outside.

When the dew point temperature is less than 50 degrees, this is considered dry, with 50 to 68 being comfortable. If it goes between 69 and 76 degrees, you are going to feel uncomfortable, so when it goes even higher than that, you’re extremely uncomfortable.

Conditions for Dew Formation

The preferred conditions to form dew come from structural characteristics and weather factors.

Preferred weather conditions include:

  • Clear night sky after a warm day
  • Very little water vapor in the atmosphere
  • Calm night with no strong winds
  • High humidity in lower air levels

Preferred structures to form dew include:

  • Well-isolated from the ground
  • Poor thermal conductivity and good radiators
  • Thin, exposed items, such as petals, grass blades, and leaves

Dew Point Temperature

The dew point temperature tells you what it’s like outside. Is it going to feel muggy and hot, or is it going to be cool and dry?

How Do You Measure It?

You can measure and calculate the dew point. It’s measured directly with a hygrometer. There are different components for such a device. You have a chamber with a mirror, light detector, and light beam. When the air within the chamber gets cooled to the dew point, dew then forms on the mirror.

The dew is just a lot of tiny water drops, and it blocks the incoming light. Then, the light detector senses the blocking of the light to indicate that the air reached the dew point. When dew forms on the mirror and blocks light, that’s the dew point temperature for the air.

Modern dew point hygrometers are about similar to a laptop’s size.

How Can You Calculate It?

It’s possible to calculate the dew point using the temperature of the air and the relative humidity value. This is measured with a sling psychrometer.

This is a metal rod and is roughly 6 inches long. There’s a thermometer on top. To get the measure, hold the base and sling around that thermometer piece. It measures the relative humidity by measuring the wet-bulb and dry-bulb temperature.

The web-bulb temperature is what the air might have it got cooled to saturation through evaporation. This is similar to the dew point.

If there were a container of air, this wet-bulb temperature is what the air might be like if the water vapor was gone. Evaporation is the cooling process, which is why people feel cold when they get out of a pool or shower. The water dissipates from the skin.

That wet-bulb of the psychrometer includes a moist sponge. When you swing it around, the water evaporates because of the movement. This cools the thermometer to the temperature reading on the wet bulb.

The faster the water evaporates, the cooler the wet-bulb temperature. This indicates the air is dry. It’s possible to use those wet- and dry-bulb temperatures to find the humidity and calculate the dew point. When you do that, you can use a chart to find the dew point temperature from the relative humidity value.

Interesting Facts about Dew

  • The theoretical maximum amount of dew for each night is 0.8mm, but it rarely goes over 0.5mm.
  • In some hot regions, dew is an essential water source. Most desert plants get 50 percent of the water they need from dew.
  • Sometimes, people confuse dew with guttation. If plants get too much water, drops at the edge and tip are formed. This is full of potassium and sugar, so if they dry, there could be a white crust on the surface.


Thanks for reading this guide. Now, you know how to calculate the dew point and what it is. Share this guide with your friends to help them learn about the weather, too!