🌬️ Air Density Calculator
Calculate the density of dry and moist air using the ideal gas law and the partial pressure method. Enter temperature, pressure, and relative humidity to get accurate air density results. Includes altitude effects and standard atmosphere reference values.
What Is Air Density?
Air density (ρ) is the mass per unit volume of Earth's atmosphere, typically measured in kg/m³. It is a fundamental property in meteorology, aeronautics, and engineering, affecting everything from aircraft lift to wind turbine efficiency.
Air density depends on three main factors:
- Temperature: Warmer air is less dense — as temperature increases, air molecules move faster and spread apart.
- Pressure: Higher pressure compresses air molecules, increasing density.
- Humidity: Moist air is less dense than dry air because water vapor molecules (18 g/mol) are lighter than the average molecular weight of dry air (28.97 g/mol).
- Altitude: Air density decreases with increasing altitude, following an approximately exponential relationship.
At sea level, 15 °C, and standard atmospheric pressure (1013.25 hPa), the standard air density is 1.225 kg/m³[reference:0].
How to Calculate Air Density
For dry air, the density is calculated using the ideal gas law:
ρ = p / (R_d · T)
where p = pressure (Pa), R_d = 287.05 J/(kg·K) for dry air, T = temperature (K)
For moist air, the total density is the sum of the partial densities of dry air and water vapor:
ρ = (p_d / (R_d · T)) + (p_v / (R_v · T))
where p_d = partial pressure of dry air, p_v = partial pressure of water vapor (both in Pa), R_v = 461.495 J/(kg·K) for water vapor[reference:1]
The partial pressure of water vapor is calculated from relative humidity and saturation vapor pressure:
p_v = RH × p_sat
where p_sat is calculated using the Magnus formula: p_sat = 6.1078 × 10^(7.5·T / (237.3 + T)) (T in °C, p_sat in hPa)[reference:2]
Why Use This Calculator?
- Instant results: Get dry and moist air density in kg/m³ with high precision.
- Humidity correction: Accurately accounts for water vapor's effect on density.
- Multiple units: Enter temperature in °C, °F, or K; pressure in hPa, Pa, kPa, bar, atm, psi, or inHg.
- Step-by-step breakdown: See exactly how the calculation is performed.
- Free & private: No registration, no data storage — all calculations are done in your browser.
❓ Air Density Calculator FAQ
What is the standard density of air?
The standard air density at sea level (15 °C, 1013.25 hPa, dry air) is 1.225 kg/m³[reference:3]. This value is used as a reference in aviation and engineering.
What is the formula for air density?
For dry air: ρ = p / (R_d · T), where R_d = 287.05 J/(kg·K). For moist air: ρ = (p_d / (R_d · T)) + (p_v / (R_v · T))[reference:4].
How does humidity affect air density?
Moist air is less dense than dry air. Water vapor (M = 18 g/mol) is lighter than dry air (M = 28.97 g/mol). At 31 °C, changing relative humidity from 30% to 90% can change air density by about 1%[reference:5].
How does altitude affect air density?
Air density decreases with altitude. An elevation change of only 82 meters from sea level can change air density by about 1%[reference:6].
What is the specific gas constant for dry air?
The specific gas constant for dry air is R_d = 287.05 J/(kg·K)[reference:7]. For water vapor, R_v = 461.495 J/(kg·K)[reference:8].
Why is moist air less dense than dry air?
Water vapor molecules have a molecular weight of 18 g/mol, while the average molecular weight of dry air is 28.97 g/mol. When water vapor displaces dry air molecules, the overall density decreases.
What is saturation vapor pressure?
Saturation vapor pressure is the pressure at which water vapor is in equilibrium with liquid water at a given temperature. It is calculated using the Magnus formula: p_sat = 6.1078 × 10^(7.5T/(237.3+T)), where T is in °C and p_sat is in hPa[reference:9].
How accurate is this calculator?
This calculator uses the CIPM-2007 compliant formula for moist air density. Accuracy depends on the precision of the input values. You can adjust the decimal precision to suit your needs.
What are the applications of air density?
Air density is critical in aviation (lift and drag), wind energy (power output), HVAC (airflow calculations), ballistics (projectile trajectories), and meteorology (weather modeling).
Is this calculator free?
Yes, this calculator is completely free to use. No registration or personal data storage is required.