Formula used
Dry air: ρ = P ÷ (Rd × T × Z)
Humid air: ρ = Pd ÷ (Rd × T × Z) + Pv ÷ (Rv × T × Z)
Pd equals total pressure minus water-vapour pressure. Absolute temperature must be expressed in kelvins.
How to use this calculator
- Select dry air, humid air, altitude-temperature, or standard-atmosphere mode.
- Enter temperature, pressure, altitude, and the preferred humidity measurement.
- Adjust gas constants, compressibility, reference atmosphere, or display precision when needed.
- Enable comparison mode to evaluate a second atmospheric condition side by side.
- Submit the form, then copy, print, or export the calculated results.
Example data
| Condition | Temperature | Pressure | Humidity | Approximate density |
|---|---|---|---|---|
| Standard sea level | 15 °C | 101.325 kPa | Dry | 1.225 kg/m³ |
| Warm humid day | 30 °C | 101.0 kPa | 70% RH | About 1.15 kg/m³ |
| Cold dry day | -10 °C | 101.3 kPa | 20% RH | About 1.34 kg/m³ |
| High altitude | 5 °C | 79.5 kPa | 40% RH | About 0.99 kg/m³ |
Frequently asked questions
What is air density?
Air density is the mass of air contained in a unit volume. It usually appears in kilograms per cubic metre.
Why does warm air have lower density?
Heating increases molecular motion and expands the air. The same mass then occupies more volume.
Does humidity increase air density?
Humidity usually lowers density at equal temperature and pressure. Water molecules are lighter than average dry-air molecules.
Why must pressure be absolute?
Gas-law calculations require pressure measured from a perfect vacuum. Gauge pressure alone does not satisfy that requirement.
What is density altitude?
Density altitude is the standard-atmosphere altitude matching the calculated density. Pilots use it to judge aircraft performance.
Can I calculate density from altitude only?
Yes. Select the standard-atmosphere mode and enter altitude. The calculator estimates pressure and temperature automatically.
What does the compressibility factor do?
It adjusts the ideal-gas result for real-gas behaviour. A value near one is common for ordinary atmospheric conditions.
Which gas constants are used?
The default dry-air constant is 287.058 J/(kg·K). The default water-vapour constant is 461.495 J/(kg·K).
How accurate is the altitude model?
The model follows a simplified standard atmosphere. Actual weather, inversions, and local pressure systems can create differences.
Can results be exported?
Yes. The result section provides copy, CSV, PDF, and print controls for convenient reporting.
Can I compare two conditions?
Yes. Enable comparison mode and enter another temperature, pressure, humidity, and altitude to see the difference.