Weather & Climate
Air density calculator.
Air density follows from temperature, pressure and humidity through the ideal gas law. Dry air at 15°C and 1013.25 hPa is 1.225 kg/m³, the standard sea-level value. Enter your conditions to get the density of moist air.
Air conditions
Air density
Fill the form and press Calculate.
Worked example
Air at 25°C (298.15 K) and 50% humidity at 1013.25 hPa. Vapour pressure is 15.84 hPa (1,584 Pa), so dry-air pressure is 99,741 Pa. Density = 99,741 ÷ (287.058 × 298.15) + 1,584 ÷ (461.495 × 298.15) = 1.1654 + 0.0115 = 1.177 kg/m³. The same air with no moisture would be 1.184 kg/m³, so humid air is slightly lighter.
How it works
Moist air is treated as a mix of dry air and water vapour, each an ideal gas: ρ = pd / (Rd T) + pv / (Rv T), with Rd = 287.058 and Rv = 461.495 J/(kg·K), T in kelvins, and pd = total pressure − pv. The vapour pressure pv is the relative humidity times the saturation vapour pressure, 6.112 × exp[17.67T / (T + 243.5)] hPa.
Water vapour is lighter than dry air (molar mass 0.018016 against 0.0289652 kg/mol), which is why more humidity lowers the density slightly.
Sources and basis (all opened 2026-10-08): Wikipedia, Density of air (ideal-gas formula, gas constants, and the ISA sea-level value of 1.2250 kg/m³ at 101.325 kPa and 15°C); saturation vapour pressure from US National Weather Service El Paso, “Dewpoint and Wet-bulb from Relative Humidity” calculator (page script: es = 6.112 × exp[17.67T / (T + 243.5)], Td = 243.5 ln(e/6.112) / (17.67 − ln(e/6.112))).
FAQ
What is the density of air?
In the International Standard Atmosphere at sea level, 15 degrees C and 101.325 kPa, dry air is 1.2250 kg/m3. Real air varies with temperature, pressure and humidity.
What is the air density at 25 degrees C, 50% humidity and 1013.25 hPa?
About 1.177 kg/m3.
Does humid air weigh less than dry air?
Yes, at the same temperature and pressure, because water vapour is lighter than the nitrogen and oxygen it displaces. At 25 degrees C and 1013.25 hPa, 50% humidity gives 1.177 kg/m3 against 1.184 kg/m3 dry.
How does altitude change air density?
Pressure falls with altitude, so density falls. Enter the actual pressure at your location to account for it.
What pressure should I enter?
The actual pressure at your location, not a sea-level-adjusted value. If you do not know it, 1013.25 hPa is a reasonable default near sea level.
What this calculates, and what it does not
Ideal-gas estimates for general information. Engineering and aviation work should use measured values and the standards that apply to it.