Absolute humidity: what it is, how it is measured and examples

Absolute humidity is the total amount of water vapor present in a given volume of air. It is normally measured in grams of water vapor per cubic meter of air (g/m³).

Unlike other types of humidity, such as relative humidity, absolute humidity does not depend on temperature, but only indicates how much water the air contains at that moment. For example, if we say that the absolute humidity is 10 g/m³, it means that in each cubic meter of air there are 10 grams of water vapor, regardless of whether it is hot or cold.

Absolute humidity is measured by calculating the actual amount of water vapor contained in a given volume of air. To do this, an instrument called a hygrometer is normally used, although not all types of hygrometers directly offer this data.

In practice, absolute humidity is usually obtained from other variables, such as air temperature and relative humidity. With these values, the exact amount of water vapor per cubic meter of air can be calculated using formulas or psychrometric tables.

For example, if a sensor measures a relative humidity of 50% and a temperature of 25°C, it can be determined that the air contains approximately 11.5 grams of water vapor per cubic meter. If the temperature increases, the air can contain more water vapor, but the absolute humidity will only change if water vapor actually enters or leaves the environment.

Let’s look at several examples that help to better understand how absolute humidity works in different everyday situations:

• On a hot, dry day: Let’s imagine the temperature is 30°C, but the air contains little water. The absolute humidity could be about 8 g/m³. This means that, even if it is hot, the air is relatively dry and the thermal sensation is not as oppressive.
• On a hot and humid day: If the temperature is still 30°C, but the air contains more water vapor, for example 20 g/m³, the absolute humidity is high. In this case, the body has more difficulty evaporating sweat, which generates a more intense sensation of heat.
• In winter: at lower temperatures, such as 5 °C, the air can contain much less water vapor, for example 5 g/m³. Therefore, although the relative humidity may seem high (above 80%), the air is still dry in absolute terms.
• Indoors with heating or air conditioning: these systems usually reduce absolute humidity, since the heated or cooled air loses some of the water vapor. That is why it is common to feel the environment drier in homes or offices with air conditioning.

In meteorology, knowing absolute humidity is key to:

• Predict rain and storms: When the air contains a large amount of water vapor, the probability of clouds and precipitation forming increases. You may be interested in this article about Storms: what they are, how they form, types and their difference from rain.
• Calculate wind chill: Water vapor influences how the body perceives heat or cold by affecting the ability of sweat to evaporate.
• Analyze the formation of fog, dew or frost: these phenomena directly depend on how much water is in the air and how it changes when it cools. Learn more about Fog: what it is and how it forms.
• Study the transport of humidity between regions: absolute humidity allows us to follow the movement of water vapor in the atmosphere, which influences the distribution of rains and droughts.

On the other hand, in climatology, absolute humidity is used to study long-term trends. For example, how climate change is altering water vapor levels in different areas of the planet. Since water vapor is a major greenhouse gas, its increase or decrease can amplify global temperature changes.

Let’s see some examples of its impact on our daily lives:

• Thermal comfort: when absolute humidity is high, the air contains more water vapor and sweat evaporates with greater difficulty. This makes the body warmer and the thermal sensation is higher. On the other hand, when humidity is low, dry air accelerates the evaporation of sweat, causing a feeling of freshness, but it can also dry out the skin or mucous membranes.
• Respiratory health: air with very little humidity can irritate the respiratory tract, dry out the throat and promote the appearance of allergies or respiratory infections. On the other hand, an excess of absolute humidity can encourage the proliferation of mites, mold and bacteria, which can also affect health.
• Conservation of objects and materials: absolute humidity influences the conservation of furniture, books, musical instruments or electronic equipment. An environment that is too humid can cause corrosion or deterioration, while air that is too dry can crack wood or damage sensitive materials.
• Agriculture and gardening: Absolute humidity levels determine the amount of water available in the air for plants. A very dry environment can cause water stress, while one that is too humid can favor fungal diseases.
• Industry and air conditioning: in factories, laboratories or air conditioning systems, controlling absolute humidity is essential to maintain air quality, avoid condensation and ensure that processes develop correctly.

Absolute humidity is the actual amount of water vapor in a given volume of air. It is expressed in grams per cubic meter (g/m³) and does not depend directly on temperature. For example, if the absolute humidity is 10 g/m³, it means that in each cubic meter of air there are exactly 10 grams of water vapor, regardless of whether it is hot or cold.

On the other hand, relative humidity is the percentage of water vapor present in the air compared to the maximum amount that air could contain at a given temperature. It is expressed as a percentage (%) and if it depends on the temperature. For example, air with 50% relative humidity at 25°C contains half the water vapor it could have before becoming saturated.

In other words, absolute humidity measures how much water there is, while relative humidity measures how close the air is to being saturated.

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