Using a Hygrometer to Monitor Indoor Humidity Levels

By: Evan Scoboria, Last updated: June 28, 2023

In our daily lives, we often neglect the importance of understanding and controlling the humidity levels in our homes. Excessive or insufficient humidity can lead to various issues, from discomfort to significant damage to your home and belongings. A hygrometer, a device that measures the moisture in the air, can be an invaluable tool in maintaining a comfortable and safe living environment. This article will guide you through understanding a hygrometer, the different types available, how to use and calibrate one, and the importance of monitoring humidity levels. By the end, you'll be well-equipped to manage your home's humidity like a pro.

A hygrometer for humidity in the air

Understanding What a Hygrometer Is

A hygrometer is an indispensable tool when it comes to assessing the humidity levels in your home. So, what exactly is a hygrometer?

In simple terms, a hygrometer is a device that measures the amount of humidity, or moisture, in the air. These devices come in various forms and sizes, some even incorporated into weather stations. Still, their primary function remains the same — to measure the relative humidity in your surroundings.

The concept of a hygrometer dates back to the 1600s, with various types and designs emerging. Modern hygrometers typically use electronic or digital technology to provide accurate readings.

Relative humidity, the measurement you get from a hygrometer, is a percentage that shows the amount of moisture in the air compared to the maximum amount the air could hold at the current temperature. If the air holds half the moisture it could contain, the relative humidity is 50%.

Understanding humidity and measuring it accurately can be crucial in maintaining comfort and health in your home. It can help you prevent problems related to overly dry or humid conditions, such as skin irritation, respiratory issues, and damage to household items. So, a hygrometer is not just a tool — it's your first defense in creating a comfortable and healthy living environment.

Types of Hygrometers

Hygrometers come in different types, each offering unique benefits and being more suitable for specific situations. Here are some of the common types:

  1. Mechanical or Analog Hygrometers: These are the traditional types of hygrometers based on mechanical principles. They often contain a human or animal hair under tension, which expands and contracts based on the humidity levels. The movement of the hair is then translated into a percentage reading.

  2. Digital Hygrometers: With the advent of technology, digital hygrometers have become increasingly common. They use sensors to measure humidity levels and offer more precise readings. These hygrometers often have additional features, such as temperature readings and memory functions, to track humidity over time. Generally, this is the type you will find available for home use. 

  3. Psychrometers: A psychrometer is a type of hygrometer that uses the principle of evaporative cooling to measure humidity. It consists of two thermometers, one of which (the wet-bulb thermometer) is wrapped in a wet cloth. As the water on the fabric evaporates, it cools the thermometer, and the difference in temperature between the wet-bulb and the dry-bulb thermometer provides a measure of relative humidity.

  4. Dew Point Hygrometers: These sophisticated devices measure the temperature at which dew forms, which can be used to determine relative humidity. They are often used in industrial and laboratory settings due to their high level of accuracy.

While some types of hygrometers offer more precision than others, the best style for you will depend on your specific needs, the level of accuracy you require, and your budget.

How to Use a Hygrometer

Using a hygrometer is fairly straightforward, but following a few steps is essential to ensure accurate readings. First, you need to place the hygrometer where you want to measure humidity. It's recommended to keep it away from direct sunlight, drafts, and other heat or cold sources, as these can impact the reading. The device should also be placed at least a few feet away from the walls, as the wall's temperature can affect the reading of the hygrometer.

Once placed in a suitable location, you can leave the hygrometer undisturbed for about two hours to acclimate to the room's environment. After this period, you can take a reading. If you're using a mechanical hygrometer, you'll need to look at the dial or pointer to see the percentage of humidity. For digital hygrometers, the device will display the reading on its screen.

Remember, a single reading is not always sufficient. Humidity levels can fluctuate throughout the day, so understand your indoor humidity comprehensively. If your hygrometer has a memory function, it can automatically record and save these fluctuations over time.

Finally, it's essential to calibrate your hygrometer periodically for accuracy's sake. You can do this by comparing it with another hygrometer known to be accurate or by using the salt test, which involves placing the hygrometer in a sealed container with a small amount of salt and water and adjusting it to read 75% humidity after several hours.

Using a hygrometer correctly ensures that you're maintaining the proper humidity levels in your home, which can contribute to a healthier and more comfortable living environment.

How to Calibrate a Hygrometer

Calibrating a hygrometer is critical to ensure that the readings it provides are accurate. Several methods for calibrating a hygrometer are used, but the salt test method is widely accepted as the most reliable. Here's how you can perform this calibration:

  1. Prepare the Test Environment: To perform the salt test, you'll need table salt, a bottle cap or small cup, a zip-top plastic bag, and your hygrometer. Start by placing a teaspoon of salt in the bottle cap or cup. Add a few drops of water to the salt to make it damp but not so much that it dissolves.

  2. Position the Hygrometer: Place the damp salt and the Hygrometer together in the zip-top bag. Ensure the hygrometer is not touching the salt or the water. Then seal the bag tightly.

  3. Wait: Leave the bag undisturbed for at least 6 hours, preferably where the temperature is stable. During this time, the salt and water will create an environment inside the bag that's about 75% relative humidity.

  4. Check and Adjust: After the waiting period, check the reading on the hygrometer without opening the bag. If it's accurate, it should read 75% humidity. If it doesn't, adjust the hygrometer (if possible) to read 75%. If your hygrometer doesn't have an adjustment feature, note the difference between the reading and 75% so you can take it into account when using the hygrometer.

  5. Verify: Repeat the test to verify the results. If the hygrometer rereads 75% humidity, it's properly calibrated.

Remember, humidity can vary with temperature, so it's best to calibrate the hygrometer at a similar temperature to where you'll use it most often. Hygrometers should ideally be recalibrated every few months to maintain their accuracy.

How to Interpret Hygrometer Readings

Interpreting hygrometer readings correctly is essential to maintaining a comfortable and healthy environment in your home. These readings tell you the percentage of relative humidity in the air, which is the amount of moisture compared to the maximum amount it could hold at the current temperature. Here's how you can make sense of these readings:

Remember, the relative humidity in your home can vary by room and season. That's why it's essential to use your hygrometer to take readings in different areas of your home and at different times of the year. If your hygrometer readings consistently fall outside the ideal 30-50% range, you may need to adjust your home's humidity levels.

The Importance of Monitoring Humidity Levels

Monitoring humidity levels in your home or office is more crucial than you realize. Humidity, or the amount of water vapor in the air, can significantly impact your comfort, health, and even the longevity of your possessions. Here's why:

Health and Comfort

When humidity levels are too high, our bodies can struggle to cool down effectively, leading to discomfort and excessive sweating. High humidity can also encourage the growth of mold and mildew, which can trigger allergies and asthma. Conversely, low humidity can lead to dry skin, sore throats, and irritated eyes.

Preservation of Belongings

Humidity can profoundly affect many of the materials found in our homes. For instance, excessive humidity can cause wood to expand and warp, damaging wooden furniture and floors. Artwork, books, and electronics are also susceptible to high and low humidity damage.

Energy Efficiency

Humidity can influence how hot or cold our homes feel. Higher humidity can make the air feel warmer, while low humidity can make it feel cooler. Maintaining an ideal humidity level can reduce the need for heaters and air conditioners, thereby saving energy.

Given these reasons, it's clear that regular monitoring and adjusting humidity levels using tools like a hygrometer can be very beneficial. Understanding what the readings mean and changing your environment allows you to maintain a more comfortable, healthier, and efficient living space.

Frequently Asked Questions

What is the ideal indoor humidity level?

The Environmental Protection Agency recommends maintaining indoor humidity between 30 and 50%. This range is generally comfortable for most people and helps prevent problems associated with high or low humidity, such as mold growth or dry skin.

How accurate are hygrometers? The accuracy of hygrometers can vary depending on the type and quality of the device. Most standard hygrometers have an accuracy range of ±3 to 5%. However, higher-end models can offer accuracy within ±1%.

Can a hygrometer measure both temperature and humidity? Yes, many hygrometers are designed to measure both temperature and relative humidity. These devices are often called thermo-hygrometers.

How often should I calibrate my hygrometer? Regular calibration can ensure the accuracy of your hygrometer readings. The calibration frequency depends on the specific device and usage, but a general guideline is to calibrate your hygrometer every 6 to 12 months.

Does a hygrometer need to be in a specific location to provide accurate readings? Hygrometers can be placed in any area where you want to measure humidity. However, for the most accurate readings, it's best to place them away from direct sunlight, drafts, heat sources, and air conditioning vents.


Hygrometers serve as invaluable tools for monitoring and controlling your home's humidity levels, helping create a comfortable and safe environment for inhabitants and belongings. By understanding what a hygrometer is, how it operates, and the importance of its use, you can effectively manage the relative humidity in your living spaces. Remember that consistent calibration is crucial for accuracy and that different types of hygrometers can offer a range of features to suit specific needs. Remember to refer to the answers to the frequently asked questions as a handy guide to using a hygrometer. By monitoring humidity, you can safeguard your home against issues associated with imbalanced humidity levels, like mold, condensation, and damage to wooden structures.