Air Density Calculator
The calculation uses a specific gas constant of 287.058 J/(kg·K) for dry air and 461.495 J/(kg·K) for water vapor.
The result is an estimate of humid air density under the entered temperature, pressure and humidity conditions.
What Is Air Density?
Air density is the mass of air contained in a given volume. It is commonly expressed in kilograms per cubic metre (kg/m³). At normal atmospheric conditions, air density is close to 1.2 kg/m³, but it changes with temperature, pressure and humidity.
Warmer air generally has a lower density than colder air because the air expands as its temperature increases. Higher atmospheric pressure increases air density, while higher humidity generally reduces the density of moist air because water vapour is less dense than the mixture of dry atmospheric gases it replaces.
How Air Density Is Calculated
The density of air can be calculated from its temperature, atmospheric pressure and relative humidity. For dry air, the ideal gas equation provides the basic relationship between pressure, temperature and density.
Temperature must be converted from degrees Celsius to absolute temperature in kelvin. When humidity is included, the total air density is calculated by accounting separately for dry air and water vapour.
Effect of Humidity on Air Density
Moist air is less dense than dry air at the same temperature and pressure. The amount of water vapour present is determined from relative humidity and the saturation vapour pressure at the given temperature.
The water vapour pressure is subtracted from the total atmospheric pressure to obtain the partial pressure of dry air. The density of water vapour is then calculated separately and added to the dry-air density.
Effect of Temperature and Pressure
Temperature and atmospheric pressure have a strong effect on air density. At constant pressure, increasing temperature decreases density. At constant temperature, increasing pressure increases density. This is why air density differs between locations, altitudes and weather conditions.
Air Density Formula
The calculation uses the ideal gas relationships for dry air and water vapour. The resulting value represents the density of the humid air under the specified temperature, pressure and relative humidity conditions.
Using Current Weather Conditions
Air density can also be estimated from current weather conditions. Temperature, atmospheric pressure and relative humidity measured at a location provide the basic inputs required for the calculation. Because these conditions change throughout the day, calculated air density can also vary with weather and altitude.