Dry air
Dry air at 1 atm from −50 to 300 °C — the ideal-gas density and Sutherland viscosity behind every duct, fan and drag calculation.
| Phase | Gas |
| Temperature range | -50 to 300 °C |
| Source | Ideal gas law with R = 287.0528 J/(kg·K); Sutherland (1893) viscosity; Incropera, Fundamentals of Heat and Mass Transfer, Table A.4 for cp and k |
Validated from -50 to 300 °C.
| Density | 1.2041 kg/m³ |
| Dynamic viscosity | 0.018133 mPa·s |
| Specific heat | 1.0069 kJ/(kg·K) |
| Thermal conductivity | 0.025696 W/(m·K) |
| Kinematic viscosity ν = µ/ρ | 15.059 mm²/s |
| Prandtl number Pr = cpµ/k | 0.7105 |
Every fluid property in these opens already filled, all from the same state — so a density and a viscosity in one calculation always describe the same fluid at the same temperature.
Reynolds Number
ρ = 1.20411μ = 0.0181332
Drag Force (F = ½CdρAv²)
ρ = 1.20411
Dynamic Pressure (q = ½ρv²)
ρ = 1.20411
Prandtl Number
μ = 0.0181332cₚ = 1.00686k = 0.0256961
Learning zone
Air density follows the ideal gas law closely enough to compute rather than look up: ρ = p/(R T) with R = 287.05 J/(kg·K). At 20 °C and one atmosphere that is 1.204 kg/m³, or 0.0752 lb/ft³ — the "standard air" behind every familiar duct constant: 1.08 for sensible heat, 4.5 for total, 0.68 for latent.
Because the density here is computed from pressure, the altitude correction is not a separate table. Air at 1500 m is about 16 % less dense than at sea level and a flue at 200 °C is 40 % of standard density. A fan is a constant-volume machine, so it still moves the same cfm — but proportionally less mass, proportionally less heat, and proportionally less brake horsepower. Denver-rated cfm against sea-level heat arithmetic is the classic mismatch.
Air viscosity runs the opposite way to water's: it RISES with temperature, from 1.46e-5 Pa·s at −50 °C to 2.93e-5 at 300 °C. In a gas, viscosity is momentum carried across a shear layer by molecules moving between layers, and heat makes them move faster. In a liquid it is intermolecular attraction, which heat breaks down. The two fluids on this page disagree about the sign of dµ/dT, and getting that backwards is a common exam loss.
Humidity moves density the other way, slightly: moist air is LIGHTER than dry air at the same temperature and pressure, because water vapour is lighter than the nitrogen and oxygen it displaces. These values are for dry air; psychrometric work needs the humidity ratio as well.
The constants library carries these at a single stated temperature, with their uncertainty and provenance. The table above is the same substance as a function.