Calculate air density, dry-air partial pressure, water vapor pressure, or temperature from any 3 inputs in Pa, psi, atm, bar, K, °C, or °F.
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Air Density Formula
The following formula is used to calculate air density for moist air using the partial pressures of dry air and water vapor (total pressure p = pd + pv).
ρ = (pd / (Rd * T)) + (pv / (Rv * T))
where:
- pd is the partial pressure of dry air in Pa,
- pv is the partial pressure of water vapor in Pa,
- 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).
Air Density Definition
Air density is the mass per unit volume of air under a given temperature and pressure (and it can also vary with humidity).
How to calculate air density?
- 1.First, determine the pressure of dry air
- This is the dry-air partial pressure pd. If you know total pressure p and water vapor pressure pv, then pd = p − pv.
- 2.Next, determine the water vapor pressure
- This is dependent on the relative humidity.
- 3.Measure the air temperature
- Measure the air temperature and convert it to Kelvin.
- 4.Calculate the air density
- Calculate the air density using the formula above.
FAQ
What is air density?
Air density is the total mass of air within a given volume.
How can air density change?
Air density can change with temperature and pressure. Increasing pressure increases density (at a given temperature). Increasing temperature decreases density (at a given pressure).
