Calculate pressure, temperature, or density for dry air from any two known values using the ideal gas law in Pa, K, and kg/m³ with unit conversions.

Pressure to Density Calculator

Enter any 2 values to calculate the missing variable (assumes ideal-gas dry air with Rspecific = 287.05 J/(kg·K)).

Density From Pressure Formula

The following formula is used to calculate the density of dry air from pressure using the ideal gas relationship. 

\rho = \frac{p}{R_{\text{specific}}\,T}
  • Where ρ is the (mass) density of dry air (kg/m^3)
  • p is the (absolute) pressure (Pa) 
  • T is the (absolute) temperature (K) 
  • Rspecific is the specific gas constant for dry air (≈ 287.05 J/(kg·K))

To calculate density from pressure (for dry air, ideal-gas approximation), divide the pressure by the product of the absolute temperature and the specific gas constant. For other gases, use that gas’s specific gas constant, or use ρ = pM/(RuT) with molar mass M and the universal gas constant Ru.

Atmospheres (atm) to Dry-Air Density (kg/m³) Conversion Table (T = 298.15 K, Rspecific = 287.05)
Pressure (atm) Density (kg/m³)
0.250.296
0.500.592
0.750.888
11.184
1.251.480
1.501.776
22.368
33.552
44.736
55.920
7.58.879
1011.839
1517.759
2023.679
2529.598
3035.518
4047.357
5059.196
7588.794
100118.393
*Assumes constant temperature T = 298.15 K (25°C) and ideal-gas dry air with Rspecific = 287.05 J/(kg·K). Calculator formula: ρ (kg/m³) = p (Pa) ÷ (Rspecific × T). Pressure converted with 1 atm = 101325 Pa.

How to Calculate Density From Pressure?

The following example problems outline how to calculate density from pressure (dry air, ideal-gas approximation).

Example Problem #1:

  1. First, determine the pressure (Pa).
    1. The pressure (Pa) is given as: 600.
  2. Next, determine the temperature (K).
    1. The temperature (K) is provided as: 100.
  3. Finally, calculate the Density From Pressure using the equation above: 

ρ = p / (Rspecific*T)

The values given above are inserted into the equation below:

ρ = 600 / (287.05*100) = 0.0209 (kg/m^3)

Example Problem #2: 

For this problem, the variables needed are provided below:

pressure (Pa) = 159

temperature (K) = 134

This example problem is a test of your knowledge on the subject. Use the calculator above to check your answer. 

ρ = p / (Rspecific*T) = ?