Air Density Calculator
Enter an absolute pressure and a temperature to get the density of dry air in kg/m³ — and see why warmer, lower-pressure air is thinner.
What is air density?
How much mass a cubic metre of air holds
This air density calculator turns two measurements — the absolute pressure in pascals and the temperature in kelvin — into the density of dry air in kilograms per cubic metre. Air density is simply how much mass is packed into a cubic metre of air. At standard sea level it is about 1.225 kg/m³, but it climbs when pressure rises and drops when the air warms, because hotter molecules move faster and spread out so fewer of them fit in the same volume. It is the number behind aircraft lift, drag on a moving car, engine power at altitude, and how far a ball or a sound carries.
Enter a pressure in pascals and a temperature in kelvin to get the dry-air density in kg/m³ instantly.
Air density follows the ideal gas law: divide the absolute pressure by the specific gas constant for dry air times the absolute temperature. The constant R = 287.05 J/(kg·K) is the universal gas constant divided by the molar mass of dry air.
ρ = P / (R × T)For the worked example, take standard sea-level conditions: a pressure of 101325 Pa and a temperature of 288.15 K (15 °C). Multiply the constant by the temperature, 287.05 × 288.15 = 82713.4, then divide the pressure by that, 101325 ÷ 82713.4 ≈ 1.225 kg/m³. Pressure pushes the density up in direct proportion, while a higher temperature in the denominator pulls it down. That is why air thins as it warms and as you climb to lower pressure.
The formula is exact for an ideal gas, but a couple of practical points are worth keeping in mind.
Dry air, absolute units, and humidity
This calculator gives the density of dry air. Real, humid air is slightly less dense at the same pressure and temperature, because water-vapour molecules are lighter than the air they replace — so in very humid conditions the true density is a little lower than the value shown. Use absolute pressure (not gauge pressure) and absolute temperature in kelvin: add 273.15 to a Celsius value, and never enter a temperature at or below 0 K.