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Humidity Vs. Relative Humidity – What is the Difference


The terms humidity and relative humidity have been used interchangeably and some people believe that both of the terms share the same meaning. Although both may mean measuring the presence of water in the air, the difference lies in the method by which the measurement is taken.

Relative humidity is important as it affects the product’s quality. Humidity on the other hand, affects the compression and granulation process.


Humidity is used to measure the amount of water in the air, usually in the form of water vapor. Also known as absolute humidity, the water is measured in grams of water per liter of air [mass/volume].

The humidity present in the air depends on the atmospheric condition of the area as well as the current season. In areas that are dry, like the desert, the humidity is low, whereas it is high in places where there are bodies of water, like rain forests and areas close to oceans. Humidity is also high during rainy season and low during summer. As the air can only hold limited amount of water, the excess moisture will turn to fog.

Relative Humidity

Relative humidity on the other hand, is a measure of the percentage of the moisture versus the highest possible moisture level present in the air at a certain temperature. Relative humidity is measured on low temperature because cold air tends to hold more water than warm air. A hygrometer is used to measure the relative humidity.

As an example, if the air measured has 50% more water vapor than it can carry, the relative humidity would be 50%, where the highest would be 100% and the lowest 0%.

We highly recommend the use of a humidity indicator in pressing arias. We have found without exception that the more humidity you have in your facility, the more problems occur in the finished products. If you are experiencing problems with humidity, you can buy dehumidifiers and fan heaters that will greatly reduce the amount of moisture in the air.

The biggest problem that will present when trying to press in a humid environment is caking. This is where the powders get stuck to each other and to the pressing surfaces. They also have a harder time flowing through the pill press or tablet press. This happens because a lot of powders are what is known as hygroscopic - they attract water out of the air.

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