What Is a Hygrometer?

A hygrometer is a measuring instruments that show how humid the air is, usually expressed as a percentage relative humidity (RF or RH). Some models also display temperature, dew point or humidity trends. There are both digital and analogue variants, and they are used in everything from homes to laboratories and industries.

An ideal indoor relative humidity ranges from around 40 to 60%, depending on a range of circumstances. When humidity levels become too high, there is a risk of mould, mites and bad odour - and if it's too low, it can cause dry skin, irritated airways and static electricity. A hygrometer will help you know the level.

How does a hygrometer work?

There are several different types of hygrometers, but the most common are electronic (digital) and mechanical (analogue).

In digital hygrometer uses sensors that measure the electrical resistance or capacitance of the air, which changes depending on how much moisture is in the air. The result is displayed on a small screen in real time, often alongside other data such as temperature, max/min values or trend arrows.

In analogue hygrometer often works with a natural hair or a synthetic material that changes length depending on the humidity level. This movement affects a pointer that shows the current level. These models are often decorative and used in the home, for example. However, they sometimes require calibration to provide a reasonably reliable value.

When is it good to use a hygrometer?

A hygrometer is useful in any situation where humidity plays a role in comfort or building condition. It helps you gain insight into a hidden problem and the opportunity to act before moisture damage occurs.

Here are some common uses:

• In the home: To avoid excessive or low humidity, which can cause dry skin, irritated airways or mould problems. Especially important during winter when the air gets drier, or in summer when humidity levels rise.
• In the cold attic and in the crawl space: Humidity is a common enemy in these spaces. A hygrometer helps you detect when the relative humidity is too high. Our crawl space dehumidifier for example, has a built-in hygrometer that displays the humidity level directly on the control panel, so you always have full control over the climate in the space.
• In greenhouses: Plants are sensitive to both too dry and too humid air. The right climate favours growth, and a hygrometer helps you create a stable environment.
• When drying: Construction projects, painting or dehumidification often require checking the moisture content of the air to ensure that materials are dry enough for further work.
• In museums and archives: Documents, paintings and historical artefacts are sensitive to moisture. Even humidity is essential to keep them in good condition.
• In recreational vehicles: Like boats, caravans or motorhomes, where fluctuating temperatures and poor ventilation easily build condensation and the risk of stale odours or mould.

💡 Tips: Place the hygrometer in the centre of the room, not directly next to a window or above a radiator, to get an accurate measurement of humidity.

Difference between a moisture meter and a hygrometer

It's easy to confuse the two, but a hygrometer and a moisture meter have different uses:

• Hygrometer: Measures humidity - how much moisture is in the air.
• Moisture meter: Measures the moisture content of materials, such as wood, concrete or walls.

While the hygrometer helps you understand if the indoor humidity is at a good level, the moisture meter shows you if, for example, a wall is dry enough to be painted or if there is a risk of mould behind the panelling. The two tools complement each other and are both useful if you want to prevent moisture damage or create a healthy indoor climate.