Quick answer
Air density combines dry air and water vapour: ρ = (p − e) ÷ (R_d T) + e ÷ (R_v T). At 1013.25 hPa, 15 °C and 0% humidity, the density is 1.225 kg/m³, the ISA sea-level standard.
Enter pressure, temperature and relative humidity. The calculator returns air density and vapour pressure.
Related tools: Density Calculator: Solve mass, density or volume. Wet Bulb Temperature Calculator: Wet-bulb temperature from air temperature and relative humidity (Stull's formula). Relative Humidity Calculator: Relative humidity from air temperature and dew point.
How to use the Air Density Calculator
- Enter pressure (hPa) (above 0).
- Enter temperature (°C) (between -80 and 60).
- Enter relative humidity (%) (between 0 and 100).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Pressure | A number, in hPa | > 0 |
| Temperature | A number, in °C | ≥ -80, ≤ 60 |
| Relative humidity | A number, in % | ≥ 0, ≤ 100 |
Formula and method
Formula
ρ = (p − e) ÷ (R_d T) + e ÷ (R_v T); e = RH × saturation pressure (Magnus)
IEEE-754 double precision; shown to the decimals indicated.
R_d = 287.058 and R_v = 461.495 J/(kg·K); saturation pressure e_s = 6.1094·exp(17.625 T ÷ (T + 243.04)) hPa.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Pressure = 1013.25; Temperature = 15; Relative humidity = 0.
| Result | Value |
|---|---|
| Air density | 1.225 kg/m³ |
| Vapor pressure | 0 hPa |
Example 2
Inputs: Pressure = 1013.25; Temperature = 30; Relative humidity = 60.
| Result | Value |
|---|---|
| Air density | 1.1533 kg/m³ |
| Vapor pressure | 25.42 hPa |
Example 3
Inputs: Pressure = 950; Temperature = 20; Relative humidity = 50.
| Result | Value |
|---|---|
| Air density | 1.1237 kg/m³ |
| Vapor pressure | 11.667 hPa |
The first line is the headline result (air density). Below it the air Density Calculator lists vapor pressure, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
What changes it
Density falls with altitude and temperature: at 30 °C the same pressure gives 1.165 kg/m³. Humid air is slightly lighter than dry air because water vapour is less dense than nitrogen and oxygen.
Uses
Aerodynamic drag, aircraft performance, wind power and engine tuning all scale with density. The formula is accurate to better than 1% for normal conditions.
How the result changes with pressure
Holding every other input at the first worked example, this table changes only pressure. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Pressure | Air density | Vapor pressure |
|---|---|---|
| 506.6 | 0.6125 kg/m³ | 0 hPa |
| 1013 | 1.2247 kg/m³ | 0 hPa |
| 2027 | 2.4506 kg/m³ | 0 hPa |
| 4053 | 4.8999 kg/m³ | 0 hPa |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Pressure: entering "0" shows "Pressure must be greater than 0." beside that field and no result.
- Relative humidity: entering "120" shows "Relative humidity must be at most 100." beside that field and no result.
Choosing between the Air Density Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Density Calculator](/science/density-calculator/) | Mass | |
| [Wet Bulb Temperature Calculator](/science/wet-bulb/) | air temperature and relative humidity | Wet-bulb temperature |
| [Relative Humidity Calculator](/science/relative-humidity/) | air temperature and dew point | Relative humidity |
| [Absolute Humidity Calculator](/science/absolute-humidity/) | temperature and relative humidity | Absolute humidity |
| [Air Changes per Hour Calculator](/science/air-changes-per-hour-calculator/) | airflow and room volume | Air changes per hour |
Background: environment and acoustics
Decibels are a logarithmic scale, so sound levels cannot be added arithmetically: two equal sources raise the level by about 3 dB, not double it. Environmental and emissions results depend on the factors behind them (for example the US EPA's equivalency factors), which are averages for a country, fuel and year.
Use the result to compare scenarios rather than as a measured value.
Assumptions and limitations
- Accurate to better than 1% for normal conditions
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for pressure and relative humidity to confirm this.
Frequently asked questions
What is standard air density?
1.225 kg/m³ at 15 °C and sea level.
Why is humid air lighter?
Water molecules weigh less than air molecules.
How does altitude change it?
It decreases roughly exponentially.
What does the Air Density Calculator calculate?
Density of moist air from pressure, temperature and humidity. It returns Air density and Vapor pressure.
What formula does the Air Density Calculator use?
ρ = (p − e) ÷ (R_d T) + e ÷ (R_v T); e = RH × saturation pressure (Magnus). R_d = 287.058 and R_v = 461.495 J/(kg·K); saturation pressure e_s = 6.1094·exp(17.625 T ÷ (T + 243.04)) hPa.
What do I need to enter in the air Density Calculator?
You enter Pressure (hPa), Temperature (°C) and Relative humidity (%).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Accurate to better than 1% for normal conditions.
What is an example of a air Density result?
With pressure 1013.25, temperature 15 and relative humidity 0, the air density is 1.225 kg/m³.
Where does the method come from?
The method follows: Alduchov & Eskridge, J. Appl. Meteor. 35 (1996) 601; specific gas constants of dry air and water vapor.
Related calculators
- Density Calculator — Solve mass, density or volume.
- Wet Bulb Temperature Calculator — Wet-bulb temperature from air temperature and relative humidity (Stull's formula).
- Relative Humidity Calculator — Relative humidity from air temperature and dew point.
- Absolute Humidity Calculator — Water vapor content of air in grams per cubic meter.
- Air Changes per Hour Calculator — Air changes per hour from airflow and room volume.
- Enthalpy Calculator — Enthalpy change of a reaction from enthalpies of formation (Hess's law), or ΔH = ΔU + pΔV at constant pressure.
Sources
- Alduchov & Eskridge, J. Appl. Meteor. 35 (1996) 601; specific gas constants of dry air and water vapor
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.