The ideal gas law rearranged to find air density from pressure and temperature — at standard sea-level conditions, this gives the well-known reference value of about 1.225 kg/m³.
How it works
Pressure is divided by the product of dry air’s specific gas constant and the absolute temperature (in Kelvin) to give density.
What this does not include
This does not include humidity — water vapor is less dense than dry air, so actual air density with significant humidity is measurably lower than this dry-air calculation.
How to use this calculator
- Enter the pressure and temperature.
A worked example
Standard sea-level pressure (101,325 Pa) at 15°C: air density = 1.225 kg/m³ — the standard reference value used throughout aviation and engineering.
What the variables mean
| Variable | Meaning |
|---|---|
| Pressure | Atmospheric pressure, in pascals |
| Temperature | Air temperature, in degrees Celsius |
Edge cases worth knowing
Higher temperature at the same pressure means lower density. Warm air expands and thins out, which is the entire principle behind hot air balloons rising.
A temperature at or below absolute zero (−273.15°C) has no physical meaning, so the calculator declines to show a result for that input.
Frequently asked questions
Why does air density decrease as temperature rises?
Warmer air molecules move faster and spread further apart at the same pressure, reducing the number of molecules packed into each unit of volume.
Why does humid air weigh less than dry air at the same conditions?
Water vapor molecules (H₂O) are lighter than the nitrogen and oxygen molecules that make up most of dry air, so replacing some dry air with water vapor actually lowers the overall density.
What’s a practical use for air density?
Aviation performance calculations, HVAC engineering, and any application where the mass of a given volume of air matters.
