Calculate Air Dynamic & Kinematic Viscosity
Uses Sutherland's law for dry air and ideal gas density. Best for engineering estimates over common atmospheric temperatures.
What this air viscosity calculator does
This calculator estimates two important flow properties of air:
- Dynamic viscosity (μ) — resistance of air to shear (units: Pa·s or cP).
- Kinematic viscosity (ν) — dynamic viscosity divided by density (units: m²/s or cSt).
If you are doing HVAC design, CFD setup, duct-flow estimates, fan performance checks, lab calculations, or Reynolds number work, these values are often required.
How viscosity changes with temperature
For gases like air, viscosity generally increases as temperature rises. This is opposite to most liquids, where viscosity decreases with higher temperature. The reason is molecular motion: hotter gas molecules transfer momentum more actively between adjacent layers of flow.
Pressure has a smaller effect on dynamic viscosity at everyday conditions, but pressure strongly affects density. Because kinematic viscosity is μ/ρ, changing pressure can noticeably shift ν.
Formulas used
1) Dynamic viscosity (Sutherland equation)
with constants for dry air:
- μ0 = 1.716 × 10-5 Pa·s
- T0 = 273.15 K
- C = 111 K
2) Density from ideal gas law
where R = 287.058 J/(kg·K), p in pascals, T in kelvin.
3) Kinematic viscosity
Quick reference values
| Temperature (°C) | Approx. Dynamic Viscosity (Pa·s) | Approx. Kinematic Viscosity at 1 atm (m²/s) |
|---|---|---|
| 0 | 1.72 × 10-5 | 1.33 × 10-5 |
| 20 | 1.81 × 10-5 | 1.50 × 10-5 |
| 40 | 1.91 × 10-5 | 1.69 × 10-5 |
| 100 | 2.17 × 10-5 | 2.28 × 10-5 |
How to use this calculator correctly
- Enter air temperature in °C.
- Enter absolute pressure in kPa (101.325 kPa for standard sea-level atmosphere).
- Click Calculate to get dynamic viscosity, density, and kinematic viscosity.
- Use kinematic viscosity in Reynolds number: Re = V·L/ν.
Engineering notes and limitations
This is an engineering approximation for dry air. At very high temperatures, unusual gas mixtures, strong humidity effects, or high-pressure real-gas behavior, use a more detailed property model or database.
For most practical atmospheric and indoor-flow calculations, this approach is reliable and widely accepted.
Summary
Air viscosity is a core parameter in fluid mechanics. With just temperature and pressure, you can quickly estimate μ and ν for real-world design and analysis. Bookmark this page and reuse it whenever you need fast, consistent air-property values.