Relative humidity: what it is, how it is measured and normal values

Relative humidity is a measure of the amount of water vapor present in the air compared to the maximum amount it could contain at a given temperature. It is expressed as a percentage.

For example, if the air has a relative humidity of 50%, it means that it contains half the water vapor it could have before becoming saturated. When the relative humidity reaches 100%, the air is completely saturated and can no longer absorb any more water vapor, which usually causes fog, dew, or rain to form.

Relative humidity is measured with an instrument called a hygrometer. There are several types, but they try to determine how much humidity there is in the air in relation to the maximum it can contain at a specific temperature.

One of the most common methods is the psychrometer, which uses two thermometers: one measures the air temperature directly (dry thermometer) and the other has a wet wick around the bulb (wet thermometer). When the water in the wet thermometer evaporates, its temperature drops. The difference between both values ​​allows you to calculate the relative humidity using a table or a formula.

Today, digital hygrometers are the most used. They work thanks to electronic sensors that detect changes in the electrical capacity or resistance of a moisture-sensitive material. These sensors send the information to a microprocessor, which displays the value on a screen instantly.

In this other article you can learn more about the Hygrometer: what it is and what it is for.

Indoors, such as homes, offices or gyms, the ideal is to maintain relative humidity between 40% and 60%. This range helps the environment feel neither too dry nor too humid.

If the humidity drops below 30%, the air becomes dry and can cause throat irritation, dry skin, dry eyes or even affect breathing. It can also generate static electricity and damage materials such as wood or paper, which tend to crack.

If the humidity exceeds 70%, the environment feels heavy and the likelihood of fungus, mold or mites appearing increases, which can cause bad odors and health problems, especially in people with allergies or asthma.

Outdoors, values ​​vary greatly depending on the weather. In coastal or tropical areas, relative humidity is usually above 70%, while in arid or inland regions it can be less than 30%.

Relative humidity directly influences people’s well-being and health, as it affects the way the body regulates temperature, breathes, and adapts to the environment. Both excess and lack of humidity can cause discomfort or even promote certain health problems.

When humidity is low (below 30%), the air becomes dry. This can cause:

• Dryness in the respiratory tract, which facilitates throat irritation and cough.
• Dry skin and lips, which may crack.
• Eye discomfort, especially in people who wear contact lenses.
• Greater susceptibility to respiratory infections, since the mucous membranes lose their natural ability to trap viruses and bacteria.

On the other hand, when humidity is high (above 70%), the air contains so much water vapor that the body cannot easily remove heat through sweat. This generates:

• Embarrassment.
• Fatigue.
• Difficulty breathing, especially in older people or people with heart or respiratory diseases.

Relative humidity in meteorology

Relative humidity is closely related to the formation of clouds, fog and precipitation. When the air reaches 100% relative humidity, it is said to be saturated, and water vapor begins to condense into small droplets, giving rise to clouds or fog. If condensation continues, it can produce rain, snow or hail, depending on the temperature.

Furthermore, this parameter is key to understanding the heat index, that is, the thermal sensation that we experience. On hot, humid days, the body sweats, but the sweat does not evaporate easily due to excess water vapor in the air. This makes us feel hotter than the thermometer actually shows. Learn more about Wind Chill: what it is, how it is calculated and factors here.

In this other post you can learn more about What meteorology is.

Relative humidity in climatology

The study of relative humidity helps to characterize different types of climate. For example, tropical regions have high levels of humidity throughout the year, while deserts are distinguished by extremely low humidity. These contrasts influence the vegetation, fauna and ecosystems of each area. In this link you can learn more about What is climatology.

We are going to give you some tips to regulate the relative humidity at home and achieve good comfort:

When the humidity is high (more than 60%)

• Ventilate daily, especially kitchens and bathrooms, where more steam is generated. Opening the windows for a few minutes each day helps renew the air.
• Use a dehumidifier, a device that removes excess water vapor from the air. Having a dehumidifier is useful in humid areas or during winter. We encourage you to learn about the best low-consumption dehumidifiers here.
• Avoid drying clothes inside the house, as evaporation increases ambient humidity.
• Check for possible leaks in faucets or pipes, and make sure that the walls do not accumulate moisture due to leaks.
• Place bags or containers of silica gel or coarse salt in closed cabinets to absorb excess moisture.

When humidity is low (less than 40%)

• Place electric humidifiers, which release water vapor in a controlled manner.
• Use containers of water near heat sources, such as radiators or stoves; When water evaporates, it humidifies the environment.
• Have indoor plants, as they release natural moisture when they sweat.
• Avoid very high heaters, which dry out the air quickly.
• Maintain good ventilation, as renewed air helps balance humidity levels.

Absolute humidity indicates the actual amount of water vapor contained in the air, regardless of temperature. It is normally expressed in grams of water vapor per cubic meter of air (g/m³). For example, if air contains 10 g of water vapor per cubic meter, that is its absolute humidity. This value only changes if water vapor enters or leaves the air, not if the temperature varies.

Instead, relative humidity compares the current amount of water vapor to the maximum amount the air could contain at a given temperature. It is expressed as a percentage (%). For example, a relative humidity of 50% means that the air contains half the water vapor it could have before becoming saturated.

If you want to read more articles similar to Relative humidity: what it is, how it is measured and normal values, we recommend that you enter our Meteorological phenomena category.