Air density calculator
This air density calculator gives the mass of air per cubic metre. At 15 °C and 1013.25 hPa (standard atmosphere) it is 1.22501 kg/m³; warm, humid air is slightly lighter.
Example: Air temperature 15 °C · Air pressure 1,013.25 hPa · Relative humidity 0 % → Result: ρ = 1.22501 kg/m³ (air density). Source: ICAO Standard Atmosphere (15 °C, 1013.25 hPa, 1.225 kg/m³); Magnus formula according to Alduchov/Eskridge (1996). Updated: .
How it is calculated
Air density is the mass of air per cubic metre. It depends on temperature, pressure and humidity, and it governs drag, wing lift, engine power and heat transfer.
How it is calculated
Dry air behaves like an ideal gas: ρ = p / (R·T), with the specific gas constant R = 287.05 J/(kg·K) and the absolute temperature T in kelvin. With humidity the water vapour is handled separately: its partial pressure pv is the relative humidity times the saturation vapour pressure ps (Magnus formula). Then ρ = (p − pv) / (R_d·T) + pv / (R_v·T) with R_v = 461.495 J/(kg·K).
Worked example
Standard atmosphere: 15 °C, 1013.25 hPa, dry. T = 288.15 K, so ρ = 101325 / (287.05 · 288.15) = 1.22501 kg/m³ (that is 0.076475 lb/ft³). At 25 °C and 60 % relative humidity, ps = 31.6174 hPa and pv = 18.9704 hPa; the density falls to 1.17555 kg/m³ compared with 1.18393 kg/m³ for dry air – about 0.7 % less.
- Water vapour (molar mass 18 g/mol) is lighter than air (29 g/mol), so humid air is thinner.
- Every 10 K of warming lowers the density by roughly 3.5 % at constant pressure.
- The calculator uses station pressure; weather reports usually quote pressure reduced to sea level.
Frequently asked questions
What is the air density at sea level?
In the standard atmosphere (15 °C, 1013.25 hPa, dry) it is 1.22501 kg/m³, rounded 1.225 kg/m³.
Why is humid air less dense than dry air?
Water vapour molecules (18 g/mol) displace heavier nitrogen and oxygen molecules (28 and 32 g/mol). At 25 °C and 60 % humidity the difference is about 0.7 %.
Which pressure should I enter?
The actual pressure at your location. It drops with altitude: at about 1000 m it is roughly 900 hPa, and the density falls accordingly.
Sources and legal basis
- ICAO Standard Atmosphere (15 °C, 1013.25 hPa, 1.225 kg/m³); Magnus formula according to Alduchov/Eskridge (1996)
- Wikipedia – Dichte der Luft (air density)
As of: · Editorial policy
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