Kinematic Viscosity of Air Calculator

Kinematic Viscosity of Air

Kinematic viscosity describes how easily air flows under gravity or pressure gradients. It combines dynamic viscosity and density into a single property used in fluid mechanics, HVAC design, and aerodynamics.

Formulas

Dynamic viscosity via Sutherland's law (T in Kelvin):

$$\mu = 1.458 \times 10^{-6} \times \frac{T^{1.5}}{T + 110.4}$$

Air density from the ideal gas law:

$$\rho = \frac{P}{R \times T}$$

Kinematic viscosity:

$$\nu = \frac{\mu}{\rho}$$

$R = 287.058\,\text{J/(kg·K)}$ for dry air. At standard conditions (20°C, 101325 Pa), kinematic viscosity is approximately $15.1\,\text{mm}^2/\text{s}$.

Practical Notes

Kinematic viscosity increases with temperature because dynamic viscosity rises faster than density decreases. This property is essential for Reynolds number calculations, boundary layer analysis, and ventilation duct sizing.

Frequently Asked Questions

What is the difference between dynamic and kinematic viscosity?

Dynamic viscosity (μ) measures internal friction in Pa·s. Kinematic viscosity (ν = μ/ρ) divides by density and is expressed in m²/s or mm²/s.

Why use Sutherland's law?

Sutherland's equation accurately models air viscosity over typical engineering temperature ranges without requiring lookup tables.

Does humidity affect the result?

This calculator assumes dry air. Humidity slightly changes density and viscosity, but the effect is small for most engineering estimates.

What units should I use for pressure?

Enter pressure in pascals (Pa). Standard atmospheric pressure is 101325 Pa.

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