Calculator Inputs
Example Data Table
These examples are generated with the same moist air density model used by the calculator.
| Scenario | Temperature (°C) | Pressure (kPa) | Relative Humidity (%) | Density (kg/m³) |
|---|---|---|---|---|
| Cold and fairly dry | 0 | 101.325 | 30 | 1.2914 |
| Mild standard air | 15 | 101.325 | 50 | 1.2211 |
| Warm humid air | 30 | 101.325 | 70 | 1.1515 |
| Hot summer air | 35 | 100.000 | 80 | 1.1113 |
| Cool high pressure | 10 | 103.000 | 40 | 1.2649 |
Formula Used
T(K) = T(°C) + 273.15
es = 611.21 × exp[(18.678 − T/234.5) × (T / (257.14 + T))]Here, T is temperature in °C and pressure is in Pa.
e = RH × es / 100
pd = p − e
ρ = pd / (RdT) + e / (RvT)Where Rd = 287.058 J/kg·K and Rv = 461.495 J/kg·K.
This approach treats air as a mixture of dry air and water vapor. It is practical for engineering, HVAC, weather, laboratory, and general physics calculations within normal atmospheric ranges.
How to Use This Calculator
- Enter the air temperature and choose its unit.
- Enter the absolute air pressure and choose its unit.
- Input relative humidity from 0 to 100 percent.
- Select your preferred output density unit.
- Choose decimal places for display precision.
- Set graph minimum and maximum temperatures in °C.
- Press Calculate Air Density to show results above the form.
- Use the CSV or PDF buttons to export the current calculation.
Frequently Asked Questions
1) What is air density?
Air density is the mass of air in a unit volume. It usually appears in kg/m³. Temperature, pressure, and humidity all change how tightly gas molecules are packed.
2) Why does humidity affect air density?
Water vapor is lighter than the average dry air mixture. As humidity rises, some dry air is replaced by lighter water vapor, so density usually falls at the same temperature and pressure.
3) Why does pressure matter so much?
Higher pressure compresses the air into less space. That increases the mass per unit volume, which raises density when temperature and humidity stay the same.
4) Which input units does this calculator support?
It supports Celsius, Fahrenheit, and Kelvin for temperature. Pressure can be entered in Pa, kPa, hPa, bar, atm, or psi. Output density can be shown in kg/m³, g/L, or lb/ft³.
5) Can I use dew point instead of relative humidity?
This version uses relative humidity directly. If you only know dew point, convert dew point to relative humidity first, then enter the resulting humidity value here.
6) Is this formula suitable for engineering work?
Yes, it is suitable for many engineering and physics tasks under normal atmospheric conditions. Extremely unusual temperatures, pressures, or precision-critical research may require a specialized thermodynamic model.
7) What does the graph show?
The graph shows how density changes with temperature while keeping your chosen pressure and relative humidity fixed. It helps you see trends instead of relying on one single calculated point.
8) Which output unit should I choose?
Use kg/m³ for science, engineering, and weather work. Use g/L when you prefer the same numeric value in a smaller unit style. Use lb/ft³ for imperial workflows.