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Relative humidity (ρ)

Air humidity refers to the proportion of water vapour in the gas mixture of the air.Humidity that is too high or too low indoors can have a negative impact on people's well-being and health.

Can be measured with:

✓ Measurable with air-Q light, air-Q basic and air-Q pro as well as air-Q science


Humidity describes the water vapour content in the air and is measured in absolute terms in g/m³ and in relative terms in %. Water vapour is not to be confused with the clouds of steam that rise from a pot of boiling water, even if the name suggests this temptation. Water vapour is gaseous water and thus, like any other component of air, invisible.

Relative humidity describes the ratio between absolute and maximum humidity. It therefore describes the ratio of the water vapour actually contained in the air to the maximum possible water vapour content and is given as a percentage.

In general, a distinction is made between absolute, relative and maximum humidity. Absolute humidity is defined as the mass of water vapour contained in a specified volume of air. Maximum humidity is the highest possible absolute humidity at a given temperature.

The lower the temperature of the air, the less water vapour it can absorb. When the air cools down, the maximum humidity can be exceeded if the previously warmer air already had a high relative humidity. Now the water condenses on the walls, floor and ceiling.

Limit values for relative humidity:

No legal limits have been set for either working or living spaces. In closed rooms, a relative humidity between 40 and 60 % is recommended. A range between 30 and 70 % relative humidity is considered acceptable. If the relative humidity exceeds 95 % or falls below 23 %, most people find the air uncomfortable.

The threshold for mould growth in rooms is exceeded at 60 % humidity. This applies with one restriction: if the exterior walls are significantly colder than the indoor air, which occurs especially in the cold half of the year.

Designationning Relative humidity limits
General recommendation Minimum value 40 %
General recommendation Maximum value 60 %

Consequences of too high or too low humidity:

If the humidity in a room is too low, breathing performance is reduced. In addition, dryness can lead to skin irritation and irritation. The mucous membranes can also dry out, which significantly increases the risk of infection from flu and colds. In extreme cases, it can lead to a frequent occurrence of nosebleeds.

If the relative humidity is too high, sweating as a means of regulating body temperature is impeded, which impairs well-being and thus performance. In addition, the circulation is strained in rooms that are perceived as humid.

In addition, there is the risk of mould growth indoors caused by high humidity. Most mould species prefer a relative humidity of 80 % at a temperature of 20 °C, although some species also develop at lower humidity. When inhaled, the spores and VOC gases of moulds can cause allergies as well as various other complaints. These include migraine, asthma, cough and cold, conjunctivitis as well as skin changes, joint pain and gastrointestinal complaints.

High humidity levels of over 60 % also lead to an increased reproduction of house dust mites. According to their increased population, these also emit more allergens, which is a particular burden for allergy sufferers.


Water vapour is produced during the evaporation of individual water molecules, which are released from the water surface with the help of thermal energy and pass into the air. This process is strongly dependent on the temperature of the water and the air. Other important factors include the size of the water surface and the degree of saturation of the air.

Humidity is created indoors by the breathing and sweating of the people and animals who live there. Cooking, showering or bathing and drying laundry also contribute to an increase in humidity. In addition, water can penetrate through leaky windows, roofs and walls, which later evaporates into water vapour. The relative humidity of a room is lowered through consistent insulation, frequent ventilation and strong heating.

Increased humidity over longer periods of time is a clear indication of water damage from heating or drinking water pipes in the partition walls.

Sensor used:

The relative humidity is measured in the air-Q by a sensor with very high accuracy. The temperature inside the air-Q is different from the temperature outside due to the self-heating of the air-Q. This self-heating also has an effect on the relative humidity measured inside the enclosure and is corrected for the outside of the enclosure using mathematical formulas. Nevertheless, the air-Q reacts somewhat more sluggishly to changes in humidity than an exposed sensor.

Measure relative humidity:

The air-Q air analyser can also measure or analyse relative humidity and other pollutants with one of its sensors. In addition, many facts about the air-Q can be found here. You can order the air quality measuring device in the online shop.

air-Q Air Quality Meter

Monitor air quality, all air components and environmental influences with the air-Q. For your health and performance.