Hygrometer: Definition, Types, Uses, and Procedures

Close up of a hygrometer

Grasping the levels of humidity present in the atmosphere is essential for numerous purposes, ranging from safeguarding historical items in galleries to ensuring the right environment in residential spaces. A hygrometer serves as a key tool in these scenarios. In this extensive guide, we'll delve into everything you need to know about hygrometers, exploring their various kinds, applications, and the proper methods to utilize them successfully.

What is a Hygrometer?

A hygrometer is a device designed to measure humidity levels in the atmosphere. It plays a vital role in ensuring that the environmental conditions are optimal for various purposes. Whether you are looking to preserve the integrity of valuable artwork, ensure the longevity of musical instruments, or simply maintain a comfortable living space, a hygrometer serves as your go-to instrument for monitoring humidity. The primary function of this tool is to measure the water vapor content in the air, providing readings that help you determine humidity levels in your environment. This data is crucial for making informed decisions to adjust the humidity to desired levels, promoting better health, comfort, and preservation of items sensitive to moisture. 

The hygrometer has come a long way since its inception. The earliest versions were rudimentary, relying on natural materials' responses to humidity changes. Over time, the technology evolved, giving rise to more accurate and reliable devices, including the popular digital and thermo hygrometer we see today.

What Does a Hygrometer Measure

A hygrometer is designed to measure the water vapor content in the air, displaying it as relative humidity, a percentage of the air's maximum moisture-carrying capacity at a specific temperature. The device can also provide vapor pressure readings in pascals (Pa), the SI unit for pressure, offering a direct measure of water vapor content. These measurements are vital for various applications, ensuring optimal conditions in living spaces, storage, and industrial processes.

Relative vs Absolute

Relative humidity and absolute humidity are two different ways of describing the amount of moisture in the air. Relative humidity is expressed as a percentage and indicates the amount of moisture the air is holding relative to the maximum amount it could hold at a specific temperature. Relative humidity gives a sense of how "full" the air is with moisture, which can be helpful for understanding comfort levels and predicting weather patterns.

On the other hand, absolute humidity is a measure of the actual amount of water vapor in the air, regardless of the air’s temperature, and is usually expressed in grams of water per cubic meter of air. Unlike relative humidity, it does not give an immediate sense of how saturated the air is, but it provides a more direct measure of moisture content.

Hygrometer Types

When it comes to choosing a hygrometer, it's essential to understand the different types available and their specific applications.

Analog vs Digital

Analog hygrometers boast a timeless appeal, utilizing the responsive nature of natural materials such as human hair or synthetic fibers to gauge changes in humidity. These devices require regular calibration and are generally considered less precise than their digital counterparts. In contrast, digital hygrometer leverages advanced electronic sensors to deliver rapid and highly accurate humidity measurements, paired with user-friendly displays that often include additional features such as temperature readings and trend indicators.

Thermo Hygrometers

Thermo hygrometer serves as an invaluable tool for both homeowners and professionals, seamlessly integrating a temperature sensor and humidity measurements into one device. This dual functionality makes them ideal for applications ranging from weather forecasting to ensuring optimal conditions in living spaces. With their ability to provide real-time data on environmental conditions, thermo-hygrometers play a crucial role in maintaining comfort and preventing issues related to improper humidity levels.


The psychrometer stands out due to its unique method of measuring humidity in open air, employing a pair of thermometers with one being covered in a wet cloth. As air passes over the wet bulb, condensation occurs and the water evaporates, causing a drop in temperature that is then used to calculate low relative humidity. This device is highly valued in fields such as meteorology and HVAC (Heating, Ventilation, and Air Conditioning) for its ability to provide accurate humidity readings without the need for electronic components.

Dew Point Hygrometers

Dew point hygrometers determine humidity by measuring the temperature at which air becomes saturated and water vapor starts to condense (dew point). They are highly accurate and are commonly used in industrial applications where precise humidity control is critical, such as in clean rooms and manufacturing processes. However, they can be more expensive and complex to operate than other types of hygrometers.

Electrical Hygrometers

This type of hygrometer gauges humidity levels by identifying shifts in the electrical resistance of a substance when it absorbs moisture from the surrounding air around it, typically utilizing salts or conductive polymers. Notable for their robustness, electrical resistance hygrometers find extensive use in industrial environments. Although they might not offer the same precision as some alternative types, their role in maintaining optimal environmental conditions is indispensable. By accurately monitoring and controlling humidity levels, these hygrometers help prevent condensation on electrical equipment, reducing the risk of short circuits and potential electrical fires.

How to Calibrate a Hygrometer

Calibrating your hygrometer ensures accurate readings, fostering precise environmental control, which is crucial in various applications. The calibration process, though differing across hygrometer types, generally entails juxtaposing the hygrometer’s readings with those of a verified humidity standard and making requisite adjustments.

For instance, to calibrate a digital hygrometer, one might use the salt test method, where a saturated salt solution in a sealed container generates a stable 75% humidity environment; after placing the hygrometer inside for a set duration, adjustments are made to align the device’s display with the expected 75% reading. Analog hygrometers, conversely, may require manual adjustments via a screw or dial on the unit after exposure to a known humidity source, ensuring their readings reflect ambient conditions accurately and reliably.

How Does a Hygrometer Work

Wet and Dry Bulb

Hygrometer utilizes the concepts of wet and dry bulb temperatures to provide accurate readings. The wet bulb thermometer is covered with a moistened cloth and provides the wet bulb temperature, which reflects the cooling effect of evaporation. This temperature is always equal to or lower than the actual air temperature.

The dry bulb thermometer, on the other hand, gives the dry bulb temperature, which is essentially the ambient air temperature without the influence of moisture. The difference between the dry bulb temperature and the wet bulb temperature is crucial to measure the relative humidity of the air. By comparing the readings between the wet bulb and dry bulb thermometer, a hygrometer can accurately gauge the moisture content in the atmosphere, helping in various applications ranging from weather forecasting to maintaining optimal indoor climates.

In essence, the wet bulb and dry bulb are two thermometers that work in tandem within a hygrometer to provide vital information about the humidity levels in the environment.

Here is a 10-step procedure to measure relative humidity using hygrometer:

  1. Choose the appropriate type of hygrometer for your needs, deciding between digital and analog models based on your specific requirements and preferences.
  2. Position the hygrometer in the location where you want to measure humidity levels, ensuring it is placed away from direct sunlight and heat sources.
  3. Allow the device sufficient time to adjust to the environmental conditions of the area, particularly if you are using an analog hygrometer.
  4. For digital hygrometers, simply read the humidity level displayed on the screen, which is presented as a percentage.
  5. If using an analog hygrometer, observe any changes in the natural or synthetic material, such as hair, used to measure humidity.
  6. Translate the observed changes in the material of the analog hygrometer into a humidity level by referring to the device’s scale or dial.
  7. Take note of the current temperature in the area since it can have an impact on the accuracy of the humidity readings.
  8. Calibrate the hygrometer as necessary, especially if it seems to be providing inaccurate readings, by following the manufacturer’s instructions.
  9. Document the humidity readings for future reference or to monitor changes over time, ensuring you have a reliable record.
  10. Regularly clean and maintain the hygrometer, adhering to the manufacturer’s guidelines, to ensure its continued accuracy and longevity.

Adjusting Humidity Levels

An ideal hygrometer reading ranges between 30-60% humidity, promoting comfort, health, and the preservation of moisture-sensitive materials. To maintain optimal conditions in various settings, it's essential to know how to adjust humidity levels effectively. In dry conditions, introducing moisture through humidifiers or water basins can help, whereas dehumidifiers or proper ventilation systems are vital in damp areas to prevent mold growth and protect materials. By utilizing hygrometers to monitor these conditions and making adjustments accordingly, one can ensure a balanced and conducive environment for a wide range of activities and purposes.

Hygrometer Applications

Weather Forecasting

Hygrometers are indispensable in meteorology, providing accurate humidity readings that contribute to weather predictions and climate studies. By measuring the moisture content in the atmosphere, these instruments help forecasters determine the likelihood of precipitation, fog, or humidity-related weather patterns. The data gathered by electronic devices is crucial for preparing weather reports that inform the public and aid in disaster preparedness.

Household Comfort and Health

In residential settings, hygrometers play a key role in monitoring and maintaining comfortable and healthy humidity levels. Proper humidity control can alleviate respiratory issues, prevent dry skin, and protect home furnishings from damage due to excessive moisture. Many homeowners use hygrometers to optimize their living spaces, ensuring a balance that promotes well-being.

Museum and Art Preservation

Museums and art galleries utilize hygrometers to safeguard precious artifacts and artwork from the damaging effects of improper humidity levels. Maintaining a stable and suitable environment is essential to preserve the integrity of historical items and artworks, preventing deterioration and ensuring their longevity for future generations. The use of hygrometers in these settings ensures that the conditions are consistently monitored and adjusted as needed.

Agriculture and Horticulture

In the fields of agriculture and horticulture, hygrometers serve to optimize growing conditions for crops and plants. By monitoring the humidity levels in greenhouses or open fields, farmers and gardeners can make informed decisions about irrigation and pest control. This not only enhances plant health and yields but also contributes to sustainable and efficient farming practices.

Industrial Processes

Various industrial processes rely on precise humidity control, and hygrometers are vital to achieving this. Industries such as pharmaceuticals, textiles, and electronics depend on accurate humidity readings to maintain quality and consistency in their products. Employing hygrometers in these environments helps prevent product defects, ensures worker safety, and contributes to overall operational efficiency.

Hygrometers are indispensable for monitoring and maintaining optimal humidity levels. Understanding the different types, how they work, and how to use them effectively ensures that you can create a comfortable and safe environment, whether at home or in a professional setting. Equipped with this understanding, you are now ready to choose the best hygrometer for your needs and use it to its full potential.

Best Hygrometer in the Market

The market offers a range of options, each with unique features and advantages. Below is a curated list of top hygrometers to help you choose the best fit for your requirements.

  • AcuRite Indoor Humidity Monitor: Known for its accuracy and reliability, this digital hygrometer also measures temperature and provides easy-to-read information. It’s affordable and user-friendly, making it a popular choice for household use.
  • ThermoPro TP50 Digital Hygrometer: This compact device offers precise humidity and temperature readings and comes with a user-friendly display. It’s known for its durability and long-lasting performance.
  • Vicks Humidity Monitor: Vicks offers a simple yet efficient hygrometer that provides quick and accurate readings. It’s widely used in homes, especially in baby nurseries, due to its trusted brand name.
  • Ambient Weather WS-10 Wireless Thermo-Hygrometer: This is a versatile option for those looking to monitor multiple locations as it supports up to eight remote sensors. It provides comprehensive data on both humidity and temperature.
  • Extech 445715 Big Digit Hygro-Thermometer: Ideal for professional use, this hygrometer provides precise measurements and features a large display for easy reading. It also includes a remote probe to measure humidity in different locations.

Frequently Asked Questions (FAQs)

What is the difference between a hygrometer and a humidity sensor?

A hygrometer is a device used to both measure humidity and display humidity levels in the air directly, while a humidity sensor is a component that detects humidity and sends signals to other electronic devices for further action or monitoring low relative humidity.

What are the advantages and disadvantages of high vs low humidity?

High humidity can lead to mold growth and discomfort, while low humidity can cause respiratory issues and damage to wooden furniture. Maintaining balanced temperatures and humidity levels is key.

Where is the best place to put a hygrometer?

The optimal location for a hygrometer depends on its intended use. For general indoor use, placing it away from direct sunlight and drafts will yield the most accurate readings.

Can a hygrometer be wrong?

Yes, hygrometers can provide inaccurate readings if they are not calibrated correctly or if they are of low quality. Regular calibration and choosing a reliable model can mitigate these issues.


The material provided in this article is for general information purposes only. It is not intended to replace professional/legal advice or substitute government regulations, industry standards, or other requirements specific to any business/activity. While we made sure to provide accurate and reliable information, we make no representation that the details or sources are up-to-date, complete or remain available. Readers should consult with an industrial safety expert, qualified professional, or attorney for any specific concerns and questions.


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Author: Herbert Post

Born in the Philadelphia area and raised in Houston by a family who was predominately employed in heavy manufacturing. Herb took a liking to factory processes and later safety compliance where he has spent the last 13 years facilitating best practices and teaching updated regulations. He is married with two children and a St Bernard named Jose. Herb is a self-described compliance geek. When he isn’t studying safety reports and regulatory interpretations he enjoys racquetball and watching his favorite football team, the Dallas Cowboys.