Air pressure

bar

Air temperature

°F

Relative humidity

%

Dew point

°F

Air density

lb/cu ft

This air density calculator lets you estimate the **ρ** parameter basing on the local temperature and pressure conditions. This value is vital for many further calculations, such as determining the aerodynamic drag forces or the performance of wind turbines. Continue reading to get a better understanding of the relationship between the local weather and ρ, and learn what air density levels can you expect in various regions.

As a mixture of gases, air doesn't have a constant density; this value depends in large on the air composition. Most components have similar densities and don't influence the overall density in a substantial way. One of the exceptions is the water vapor; the more water vapor in the air, the lower its density.

For dry air at sea level at a temperature of 15°C, the density is approximately equal to 1.225 kg/m³. If you change the air temperature, humidity, or the altitude (and hence the pressure), the air density will change, too. As a rule of thumb, you can expect a drop of 0.11-0.12 kg/m³ per 1000 m of altitude change.

To find the air density at any given location, you will need some basic weather parameters. You can usually find them at the website of your local weather station.

**Air pressure**: the barometric pressure expressed in hPa. If the analyzed location is at a high altitude, you can use our air pressure at altitude calculator to establish a more accurate value for this parameter.**Air temperature**: simply, the outside temperature in °C.**Relative humidity**or**dew point**: our air density calculator is able to use one of these values to compute the other, so you only need to know one of them. Dew point is measured in °C, as it is the temperature below which the water vapor starts to condensate.

The method of finding the air density is quite simple. You have to divide the pressure exerted by the air into two partial pressures: of the dry air and of the water vapor. Combining these two values gives you the desired parameter.

- Calculate the saturation vapor pressure at dew point
*T*, using the formula`p₁ = 6.1078 * 10^[7.5T /(T + 237.3]`

. Saturation vapor pressure means that the relative humidity is equal to 100%. - Find the actual vapor pressure, multiplying this value by the relative humidity:
`pv = p₁ * RH`

. - Subtract the vapor pressure from the total air pressure to find the pressure of dry air:
`pd = p - pv`

. - Input the calculated values into the following formula:

`ρ = (pd / (Rd * T)) + (pv / (Rv * T))`

where:

`pd`

is the pressure of dry air in hPa,`pv`

is the water vapor pressure in hPa,`T`

is the air temperature in Kelvins,`Rd`

is the specific gas constant for dry air equal to 287.058 J/(kg·K), and`Rv`

is the specific gas constant for water vapor equal to 461.495 J/(kg·K).

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