Air Density Calculator
Calculate the density of air from temperature, atmospheric pressure, and relative humidity. Essential for aviation, HVAC, ballistics, motorsport, and atmospheric science.
Atmospheric Conditions
Enter temperature, pressure, and humidity to calculate air density
Standard atmosphere: 15 °C (59 °F / 288.15 K). Higher temperatures produce lower air density.
Standard sea-level pressure: 101,325 Pa (1013.25 hPa / 1 atm). Decreases with altitude.
Humid air is less dense than dry air. Moist air displaces heavier N₂ and O₂ with lighter H₂O molecules.
Air Density Result
Density, partial pressures, and atmospheric properties
Enter your atmospheric conditions above and click Calculate Air Density to see the result.
Air Density Formulas
The equations used by this calculator, based on the ideal gas law and Tetens’ formula for saturation vapour pressure.
Moist Air Density
+ (Pv / (Rv × T))
The core formula. Pd = partial pressure of dry air; Pv = partial pressure of water vapour; T = temperature in Kelvin.
Saturation Vapour Pressure
7.5 × Tc / (237.3 + Tc)) × 100
Tetens’ formula estimates the maximum water vapour pressure at temperature Tc (°C). Result in Pascals.
Partial Pressure of Vapour
The actual water vapour pressure, where RH is relative humidity (0–100%). Pv approaches Psat at 100% RH.
Partial Pressure of Dry Air
Total atmospheric pressure minus the vapour pressure gives the pressure contributed by dry air molecules only.
Gas Constants
Rv = 461.495 J/(kg·K)
Rd is the specific gas constant for dry air; Rv is for water vapour. Both derived from the universal gas constant R = 8.314 J/(mol·K).
Dry Air Approximation
For dry air (RH = 0%), the formula simplifies to this. At ISA sea-level conditions, this gives ρ = 1.2250 kg/m³.
Air Density at Common Conditions
Dry air density at sea-level pressure (101,325 Pa) across a range of temperatures. All values rounded to four decimal places.
| Temperature (°C) | Density (kg/m³) | Density (lb/ft³) | Typical Condition |
|---|---|---|---|
| −40 | 1.5141 | 0.09451 | Extreme winter cold |
| −20 | 1.3944 | 0.08703 | Arctic winter |
| −10 | 1.3413 | 0.08372 | Cold winter day |
| 0 | 1.2922 | 0.08066 | Freezing point |
| 5 | 1.2690 | 0.07921 | Cool spring |
| 10 | 1.2466 | 0.07782 | Mild day |
| 15 | 1.2250 | 0.07648 | ISA standard (sea level) |
| 20 | 1.2041 | 0.07517 | Comfortable room temp |
| 25 | 1.1839 | 0.07391 | Warm summer day |
| 30 | 1.1644 | 0.07270 | Hot summer |
| 35 | 1.1455 | 0.07152 | Very hot day |
| 40 | 1.1272 | 0.07038 | Extreme heat |
Air Density FAQ
Everything you need to know about air density, how it is calculated, and why it matters in aviation, sport, and engineering.
Air density is the mass of air contained in a given volume, expressed in kg/m³ or lb/ft³. At sea level under standard ISA conditions (15 °C, 101,325 Pa, 0% humidity), dry air has a density of approximately 1.225 kg/m³. Density decreases with altitude, rising temperature, and increasing humidity.
Air density and temperature are inversely related. As temperature rises, air molecules gain kinetic energy and spread further apart, reducing the number of molecules per unit volume — and therefore mass. Cold air is always denser than warm air at the same pressure, which is why hot air balloons rise and why winter air feels “thick” in aviation terms.
This surprises many people. Water vapour (H₂O) has a molar mass of 18 g/mol, while the nitrogen (N₂, 28 g/mol) and oxygen (O₂, 32 g/mol) it displaces are much heavier. When water vapour molecules replace denser gas molecules, the average mass per unit volume drops — meaning humid air is genuinely lighter than dry air at the same temperature and pressure.
For moist air: ρ = (Pd / (Rd × T)) + (Pv / (Rv × T)), where Pd is the partial pressure of dry air, Pv is the partial pressure of water vapour, T is temperature in Kelvin, Rd = 287.058 J/(kg·K) is the specific gas constant for dry air, and Rv = 461.495 J/(kg·K) is the specific gas constant for water vapour. Saturation vapour pressure is calculated using Tetens’ approximation formula.
The International Standard Atmosphere (ISA) defines standard sea-level air density as 1.225 kg/m³ (0.07651 lb/ft³). These conditions are 15 °C (59 °F), 101,325 Pa (1 atm), and 0% relative humidity. This value is used as the baseline in aviation performance calculations, aerodynamic design, and engine ratings worldwide.
In aviation, lower air density reduces the lift generated by wings and the thrust produced by engines. Aircraft require longer runways at high-altitude or hot airports. In cricket, football, and golf, lower density means less aerodynamic drag — balls travel further in hot, high-altitude stadiums (Mexico City at 2,240 m is a well-known example). In motorsport and cycling, lower air density reduces both drag on the vehicle and the oxygen available for engine combustion.