How to Measure Humidity

Posted in: Measuring Weather

How to Measure Humidity

This article was originally published in 2017 and has been updated in 2021 to include relevant products and details.

How is Humidity Measured?

To measure the amount of moisture in the air, use a humidity monitoring device called a hygrometer.

What is Humidity?

Humidity is the amount of water vapor (water that has turned from a liquid to an invisible gas) in the air. Absolute humidity is the actual amount of water vapor in a specified volume of air. Relative humidity is the ratio of moisture in the air as compared to the maximum amount of moisture the air can hold, which varies depending on the air temperature. Hotter air, for example, can hold more moisture.

Why is Humidity Important?

Humidity affects the way we perceive a given temperature – in other words, at the same temperature, higher humidity will generally make us feel warmer, and lower humidity will make us feel cooler. This is because our bodies’ cooling mechanism is perspiration, and when the air holds more moisture, the dampness on our skin can’t evaporate as easily.

Knowing the relative humidity indoors is important because humidity affects comfort, health, and the condition of household possessions. When indoor humidity is too high (above 55%), people tend to consider the room to be hot and stuffy even though the temperature may be at a level that is normally comfortable. When the indoor humidity drops below 25%, the dry air also reduces comfort. Keeping humidity in the optimal range indoors helps to control bacteria, viruses, fungi (including mold), allergies, and asthma. Humidity monitoring provides a way to check how well humidifiers, dehumidifiers, and air conditioners are working. Proper humidity control can also help equipment performance and reduce energy consumption.

Outdoor humidity also makes a difference in what a particular temperature feels like. It is more difficult for our bodies to handle hot weather when the humidity is high. While unfortunately humidity control is impossible outdoors, knowing the relative humidity level can help us to understand how warm or cool the air will feel at a given temperature. Using a humidity monitoring device outdoors can also alert you to rain, snow, or reduced visibility. When the relative humidity is 100%, the air becomes saturated, meaning it can’t hold any more moisture at that temperature. If it cools down even a little, the air will release water in the form of dew on the ground, fog or mist in the air, or precipitation from the clouds.

Using Hygrometers to Measure Humidity

A humidity monitoring device is called a hygrometer. Hygrometers may be designed for indoor or outdoor humidity monitoring use (or both). Below is a summary of the types of hygrometers available for measuring humidity.

Types of Hygrometers

1. Analog Hygrometer

Analog hygrometer mounted on a wall next to a wooden chair

Analog hygrometers use a moisture-sensitive material that is attached to a coil spring. The spring controls a needle on an easy-to-read circular dial. Analog hygrometers are often part of a durable, weather-resistant device that also includes a thermometer.

The advantages of analog hygrometers are that they are generally inexpensive and simple to use. When combined with a thermometer, they provide useful information about the weather or indoor conditions at a glance. Analog thermometer-hygrometer combinations come in different sizes, shapes, and finishes to complement your decor. Sometimes analog hygrometers are combined with an attractive clock or a classic weather station that displays environmental conditions including relative humidity. The hygrometer dial on these types of hygrometers is typically marked to indicate optimal and problematic humidity levels.

Analog hygrometers are not as accurate as digital devices. They generally measure to within ±10% accuracy. They also are slow to reflect abrupt changes in humidity, sometimes taking up to an hour to reach an accurate reading. While AcuRite hygrometers are individually hand-calibrated and typically should require no further adjustment, should you need to calibrate your analog hygrometer, it is important to follow the included instructions carefully.

2. Digital Hygrometers

Digital hygrometer in a child's room

Digital hygrometers determine the relative humidity by using a sensor to monitor an electric current that is affected by moisture levels. They are often integrated into multifunction weather measurement devices, ranging from simple indoor temperature and humidity monitors to indoor/outdoor devices with multiple features.

Digital hygrometers can keep track of high and low humidity measurements, historical data, and trends. They are more precise than analog hygrometers, with a typical accuracy range of ± 5%. Digital humidity devices do not require manual recalibration; some allow manual calibration for fine-tuning.

Basic digital hygrometers have an LCD display that shows temperature and relative humidity, and they may include additional information such as optimal comfort ranges and daily highs and lows. Depending on the model, they may be mounted on a wall, set on a level surface, or even magnetically attached to the refrigerator for easy reference.

3. Weather Stations with Hygrometers

AcuRite Weather Station sitting on a countertop in a bright room

Digital weather stations include an outdoor sensor that transmits data wirelessly to an indoor LCD console, making it possible to measure both indoor and outdoor humidity levels, along with other environmental and weather data. Digital weather stations may include a selection of features including the weather forecast, an atomic clock, and a moon phase indicator.

For easy indoor humidity observation, some AcuRite weather stations include a Humidity Level Icon, to easily indicate a high, low, or ideal indoor humidity level. For outdoor weather observations, all AcuRite professional digital weather stations include hygrometers to measure relative humidity. They also measure such conditions as temperature, atmospheric pressure, rain, wind speed, and wind direction.

4. Monitor Humidity Sensors with MyAcuRite®

AcuRite’s premier Temperature and Humidity Environment Systems include an indoor or outdoor wireless sensor and AcuRite Access®, which captures environmental data, historical records and trends, and allows for remote monitoring online at MyAcuRite or by using the free My AcuRite Apple iOS or Android apps.

AcuRite has the humidity monitoring tools to keep you and your family comfortable inside your home with indoor room sensors as well as outdoor weather stations with hygrometers.  Stay informed and keep an eye on your home and valuables even when you are traveling with My AcuRite remote monitoring. 

Join the conversation: Share your home monitoring success stories below! 

April 9, 2021
Alex Turner
March 13, 2018
Thanks for sharing such a nice post. Your post is informative and helpful. Indoor Humidity Monitor can help us to know our home environment. if humidity rise/down, we can regain it. The monitor also shows temperature. I am using AcuRite 00326 Home Comfort Monitor.
February 2, 2019
Nice post!! thanks for this wonderful post on this blog. I loved reading this blog. very useful and informative blog.
July 24, 2019
Informative. Thanks a lot!
Dave Yuhas
September 7, 2019
When I was studying horticulture/greenhouse management I was taught that a hygrometer needed moving air to be accurate.
September 11, 2019
Humidity is playing the important role in our home, warehouse and for environment. We can control the humidity with accessing of Wireless Humidity Sensors, these sensors helps in control and track the humidity level in our home and warehouse. Thanks for sharing!
Sam Nahar
October 6, 2019
Wonderful post. This information is very informative and very helpful. Looking forward to more great articles.
Joseph Karl Houseman
November 2, 2019
My Acurite outdoor sending unit got waterlogged after a severe storm. I removed the back and dried it out with a hair dryer. It now records temperature fine but shows 95% humidity. Will this eventually dry out and begin to read correctly or do I need a new outdoor unit?
AcuRite Team
November 4, 2019
We have reached out to you via email to discuss your situation further. Please check your inbox and get back to us when you have the chance!
Danny Lanier
November 11, 2019
My new Acurite, purchased from Amazon, shows a humidity of 44% but the indicator says that is a low level. It should be OK, per info from another part of this site. Should I send this back?
AcuRite Team
November 12, 2019
The humidity level comfort icon on AcuRite products also takes the temperature into account when deciding whether it should indicate HIGH, OK, or LOW Humidity. If the humidity is between 25% and 55% and the temperature is within 65-73 degrees Fahrenheit/18-23 degrees Celsius the device will indicate that the humidity level is OK. If the readings were to drop below 65 degrees Fahrenheit/18 degrees Celsius or 25% humidity the device would indicate LOW humidity. If the levels rise above 73 degrees Fahrenheit/23 degrees Celsius or 55% humidity, the device would indicate HIGH humidity. If your unit is not operating within these guidelines or you have any questions, please feel free to reach out to our support team via live chat or email request.
David Harp
November 30, 2019
Which monitor is best to monitor humidity in a crawl space and how many monitors do you recommend?
AcuRite Team
December 3, 2019
In order to monitor a crawl space, you will want a unit with an external sensor and a separate display unit so that you can monitor the conditions. We offer multiple units that would suit your needs. If you are looking to monitor more than one area with a single display unit, I recommend one of our Multi-Sensor Stations. Our support team would be happy to assist you in finding the perfect station to suit your needs! You can contact us via live chat or email request on our Support website.
Mausam Sharnagat
May 3, 2020
This a usefull article, what is the definition of humidity? I hard this question many time and I get answer from here : what is the simple definition of humidity (latest information 2020)
Barb Jarrell
September 8, 2021
Our hardwood floors are crackling and cracking. We have been working with the di humidifier company for over a year. The crawl space humidity averages 45-52. The indoor humidity reading averages 37/43%. We have had several flooring companies telling us if we do not get the interior moisture up our floors are going to buckle, crack and pop etc. Flooring companies stated the hardwood was not accumulated long enough or not installed correctly. My concern is today the meter read 40% in the house and the temperature never matches the Honeywell meter. What should the indoor humidity be at? Thank you.
AcuRite Team
September 8, 2021
The following article may be helpful in determining an appropriate humidity level!
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