Calculate the density of moist air from its temperature, pressure (or altitude) and humidity. Get the result in kg/m³ and lb/ft³, compare it with the 1.225 kg/m³ sea-level standard, and see how it changes with temperature, which is useful for cycling, drones, wind turbines, ballistics and HVAC.
Last updated:
Pressure from
absolute pressure, not corrected to sea level (unless you chose sea-level + altitude)
%
Enter your values to see the result.
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How to use the Air Density Calculator
Choose where the pressure comes from: a barometer, your altitude, or the weather report's sea-level pressure plus altitude.
Enter the air temperature in °C or °F.
Enter the pressure and/or altitude in the unit you have.
Enter the humidity as relative humidity or dew point (0% for dry air).
Press Calculate to see the density, the comparison with standard air and the working.
Air density table at sea-level pressure (1013.25 hPa)
Temperature
Dry (kg/m³)
50% RH (kg/m³)
100% RH (kg/m³)
Dry (lb/ft³)
-20 °C (-4 °F)
1.3944
1.3941
1.3937
0.08705
-10 °C (14 °F)
1.3414
1.3407
1.3400
0.08374
0 °C (32 °F)
1.2923
1.2908
1.2893
0.08067
10 °C (50 °F)
1.2466
1.2438
1.2409
0.07783
15 °C (59 °F)
1.2250
1.2211
1.2172
0.07648
20 °C (68 °F)
1.2041
1.1989
1.1936
0.07517
25 °C (77 °F)
1.1839
1.1769
1.1700
0.07391
30 °C (86 °F)
1.1644
1.1552
1.1460
0.07269
35 °C (95 °F)
1.1455
1.1335
1.1215
0.07151
40 °C (104 °F)
1.1272
1.1117
1.0962
0.07037
Standard atmosphere by altitude
Altitude
Pressure
Temperature
Density (kg/m³)
% of sea level
0 ft (0 m)
1013.2 hPa
15.0 °C
1.2250
100.0%
1,000 ft (305 m)
977.2 hPa
13.0 °C
1.1896
97.1%
2,000 ft (610 m)
942.1 hPa
11.0 °C
1.1549
94.3%
3,000 ft (914 m)
908.1 hPa
9.1 °C
1.1210
91.5%
5,000 ft (1,524 m)
843.1 hPa
5.1 °C
1.0556
86.2%
7,500 ft (2,286 m)
767.1 hPa
0.1 °C
0.9779
79.8%
10,000 ft (3,048 m)
696.8 hPa
-4.8 °C
0.9046
73.8%
15,000 ft (4,572 m)
571.8 hPa
-14.7 °C
0.7708
62.9%
Standard-atmosphere values for dry air. Real density on a given day depends on the actual temperature, pressure and humidity, which is what the calculator uses.
How the calculation works
Air is treated as a mixture of two ideal gases. The water vapor pressure comes from the humidity via the Magnus formula es(T) = 6.1094 × exp(17.625 T ÷ (T + 243.04)) hPa. The dry-air part and the vapor part are each divided by their gas constant and the absolute temperature, then added. This matches the more detailed CIPM-2007 air density equation to within about 0.1% for normal weather conditions.
Frequently asked questions
What is the formula for air density?
For moist air, ρ = P_d ÷ (R_d × T) + e ÷ (R_v × T), where P_d is the dry-air partial pressure in pascals, e the water vapor pressure, T the temperature in kelvin, R_d = 287.05 J/(kg·K) and R_v = 461.495 J/(kg·K). For dry air it reduces to the ideal gas law ρ = P ÷ (R_d × T).
What is the density of air at sea level?
The International Standard Atmosphere uses 1.225 kg/m³ (0.0765 lb/ft³) for dry air at 15 °C and 1013.25 hPa. Real air at sea level ranges from about 1.15 kg/m³ on a hot day to over 1.3 kg/m³ in very cold weather.
Does humidity make air denser or lighter?
Lighter. A water molecule (18 g/mol) is lighter than the average dry-air molecule (about 29 g/mol), so replacing some dry air with water vapor at the same temperature and pressure lowers the density, usually by around 0.5–2% on warm humid days.
How does altitude affect air density?
Pressure falls with height, so density drops too: about 9% lower at 1,000 m (3,300 ft) and about 22% lower at 2,500 m (8,200 ft) in the standard atmosphere. That reduces aerodynamic drag, engine power, propeller thrust and wind turbine output.
Should I enter station pressure or sea-level pressure?
Density depends on the actual pressure where the air is. Weather reports give pressure corrected to sea level, so at altitude choose "Sea-level pressure + altitude" and the calculator converts it. A home barometer that has not been set to sea level reads station pressure.
Why do cyclists and engineers care about air density?
Aerodynamic drag, lift and wind power are all proportional to air density. A 5% drop in density cuts drag on a cyclist by 5%, and wind turbine power P = ½ ρ A v³ also falls by 5%, so it is used for performance estimates, ventilation design and ballistics.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.