What is air density?

Air density is defined as the mass of air contained in a certain volume; it tells you how heavy or dense the air is. The unit for this is: kg/m³ (kilograms per cubic meter). Air density is not a constant value, it changes depending on the temperature, altitude and humidity which is why an air density calculator is very useful for fan manufacturers as it will determine the actual density of air under real-world conditions. The performance of a fan depends directly on the density of the air being moved. Since air density changes with temperature, altitude and humidity, the same fan can deliver different airflow, pressure and power values in different air environments. Lower density air is thinner and will have less resistance whilst higher density air is heavier and contains more oxygen per volume.

How does temperature, altitude and humidity affect air density?

If you have a higher temperature, the air molecules move faster which means air expands so density decreases whereas if you have a lower temperature, air molecules move slower so the air contracts and the density will increase.
As altitude increases, the atmospheric pressure decreases and with a lower pressure there are less air molecules which means a lower density. Whereas if the altitude decreases, there is a higher pressure and higher density in the same volume of air.
Humidity is the amount of water vapour in the air, so when the humidity increases the water vapour replaces heavier gases so the air density decreases.

The air density calculator will help you find the air density from its main three constituent parameters of temperature, elevation and relative humidity.