Air Viscosity

Follow us on Twitter
Question, remark ? Contact us at contact@myengineeringtools.com

1. Air viscosity at ambient temperature
2. Air Viscosity in between -100 and 500°c
3. Air viscosity variation with pressure
4. Detailed Viscosity Data & Practical Engineering Applications
5. Air‑Viscosity Calculator (Sutherland’s Law)

1. Air viscosity at ambient temperature

What is the viscosity of air ?

The viscosity of air, at atmospheric pressure is the following :

Air viscosity at 0°c = 0.01722 mPa.s
Air viscosity at 25°c = 0.0186 mPa.s

2. Air viscosity in between -100 and 500°c

How the air viscosity change with temperature ?

The air viscosity depends on the temperature and is increasing with the temperature. The evolution of air dynamic viscosity with the temperature is illustrated by the graph below.

Dynamic viscosity of air versus temperature (Sutherland’s law)

3. Variation with pressure

How the air viscosity vary with pressure ?

The viscosity is increasing with the pressure. To estimate the viscosity of air according to the pressure, abacus using reduced pressure and reduced temperature can be used for an estimation.

4. Detailed Viscosity Data & Practical Engineering Applications

The dynamic viscosity of air varies predictably with temperature. The most widely‑used representation is Sutherland’s law, which provides an accurate (< ± 2 %) estimate for ordinary pressures and a broad temperature range [0][1][2]. Using the reference values µ₀ = 1.716 × 10⁻⁵ Pa·s at T₀ = 273.15 K and the Sutherland constant S ≈ 110.4 K, the table below lists the dynamic viscosity (µ) from –100 °C to 500 °C. Values are expressed in µPa·s (1 µPa·s = 10⁻⁶ Pa·s) for easier comparison with typical engineering data [0].

Temperature (°C)	Dynamic Viscosity µ (µPa·s)
-100	11.7
0	17.2
25	18.4
100	21.7
200	25.7
300	29.3
400	32.5
500	35.5

Typical Engineering Scenarios Where Air Viscosity Is Critical

Duct‑flow Reynolds number – Determines laminar vs. turbulent regime.
Example: 0.5 m diameter ventilation duct, air at 20 °C (ρ ≈ 1.204 kg·m⁻³, µ ≈ 18.1 µPa·s). With a mean velocity of 5 m·s⁻¹, Re = ρ V D / µ ≈ 1.204·5·0.5 / 1.81×10⁻⁵ ≈ 1.66 × 10⁵ → fully turbulent.
Pressure‑drop calculations (Darcy–Weisbach) – The friction factor depends on Reynolds number, which in turn uses µ. Accurate µ values improve pump/fan sizing.
Heat‑transfer correlations (e.g., Dittus‑Boelter, Gnielinski) – Both Nusselt and Prandtl numbers require µ (through ν = µ/ρ). This is essential for HVAC coil design, electronic cooling, and gas‑turbine blade cooling.
Aerodynamic drag & lift predictions – In CFD and wind‑tunnel simulations, the air’s viscosity sets the viscous sub‑layer thickness and influences boundary‑layer separation.
Spray‑drying & particulate transport – Viscosity controls the Stokes number, affecting particle settling and residence time in dryers or cyclones.

5. Air‑Viscosity Calculator (Sutherland’s Law)

Temperature (°C)

Sources

#	Source	Title / Description	URL
0	Engineers Edge	Viscosity of Air, Dynamic and Kinematic – Provides standard dynamic‑viscosity values (e.g., 18.6 µPa·s at 25 °C) and a concise summary of Sutherland’s law.	https://www.engineersedge.com/physics/viscosity_of_air_dynamic_and_kinematic_14483.htm
1	MyEngineeringTools (Air Psychrometrics)	Air Viscosity – Values of air viscosity at usual temperatures – Offers a temperature‑viscosity table that matches the data used in the article.	https://myengineeringtools.com/Air/Archives/Air_Viscosity.html
2	Reddit / r/AskEngineers	Discussion: Reliable source for dynamic viscosity tables of air and water – Confirms that Sutherland’s law is the accepted method for calculating air viscosity across a wide temperature range.	https://www.reddit.com/r/AskEngineers/comments/v5rw04/about_a_reliable_source_for_dynamic_viscosity/