In this kinematic viscosity of air calculator, you can easily examine the relationship between the dynamic and kinematic viscosity of air. Viscosity is an important property of fluids and gases, especially if you consider aerodynamic problems. Both viscosity terms are interconnected. For example, you can determine the kinematic viscosity of air if the dynamic viscosity and density are already known.
In this calculator, we will learn more about viscosity, with a particular focus on the kinematic and dynamic viscosity of air. Keep reading to learn:
- What does viscosity mean?
- How to calculate the kinematic and dynamic viscosity of air?
- What does the viscosity of air depend on?
- What is the viscosity of air at 20 degrees Celsius? What is the viscosity of air at sea level?
What does viscosity mean?
Imagine an object moving in slow motion through the air. Aerodynamic forces are created between the air and the object because the air molecules near the object will become disturbed and move around the object. The magnitude of these forces depends on the object's shape and velocity, the gas's mass, and two other important properties of the air: viscosity and compressibility.
When an object moves in a gas, the gas molecules stuck to its surface form moving surfaces between which friction is created. Viscosity tells us how much resistance air has to flow and how resistant it is to gradual deformation under stress. We can distinguish two types of viscosity: dynamic and kinematic viscosity of the air.
💡 We are using the same terms to describe viscosity both in air and liquids because air and all other gasses can be considered fluids. Their molecules are in constant motion, and they flow as in liquids. For comparison, check the water viscosity calculator.
Dynamic viscosity of air
A dynamic viscosity (or absolute viscosity) is generated if we have different surfaces of air molecules moving parallel to the object's surface. This results in a shear force. To overcome the resistance of the fluid, an external force F must be applied per unit of moving surface. The magnitude of F is proportional to the speed v and the area A of the moving surface and inversely proportional to their separation y:
F = μ · A · (v / y)
The dynamic viscosity μ (Greek letter mu) is the proportionality coefficient in this formula, and we can express it in SI units:
μ = kg/(m·s) = N·s/m² = Pa·s
In practice, we can use the following empirical formula (Sutherland's law) for engineering purposes:
μ = (1.458 × 10−6 × T3/2) / (T + 110.4)
where:
- 1.458 × 10−6 — constant (kg/(m·s·√K));
- T — absolute temperature in Kelvin; and
- 110.4 — Sutherland's constant (another empirical constant) in Kelvin.
Kinematic viscosity of air
Kinematic viscosity (marked with the Greek letter nu, ν) describes a relationship between dynamic (absolute) viscosity and air density. You can obtain the kinematic viscosity of air by dividing dynamic viscosity by the density ρ:
ν = μ / ρ
The density of air itself follows the ideal gas law:
ρ = P / (R · T)
where P is the absolute pressure (Pa), R = 287.058 J/(kg·K) is the specific gas constant for dry air, and T is the absolute temperature (K). Kinematic viscosity is expressed in:
- Metric (SI): m²/s (also commonly mm²/s = cSt, centistokes)
- American (Imperial): ft²/s (square feet per second)
How to use the kinematic viscosity of air calculator?
- Select your preferred unit system — Metric (°C, hPa) or American/Imperial (°F, psi).
- Enter the air temperature in the selected unit.
- Enter the air pressure (the default 1013.25 hPa / 14.696 psi is standard sea-level pressure).
- Click Calculate. The calculator instantly displays:
- Dynamic viscosity in Pa·s, mPa·s (= cP) and lbf·s/ft²
- Kinematic viscosity in m²/s, mm²/s (= cSt) and ft²/s
- Air density at the given temperature and pressure
- The applied formulas with computed values
Effect of temperature on the viscosity of air
Unlike liquids, the viscosity of a gas increases with temperature. As air gets hotter, its molecules move faster and collide more often, transferring more momentum between layers — which raises the dynamic viscosity. The table below shows representative values at standard sea-level pressure (1013.25 hPa).
| Temperature (°C) | Temperature (°F) | Dynamic Viscosity μ (Pa·s) | Kinematic Viscosity ν (m²/s) | Density ρ (kg/m³) |
|---|---|---|---|---|
| -25 | -13 | 1.583 × 10⁻⁵ | 1.137 × 10⁻⁵ | 1.394 |
| 0 | 32 | 1.715 × 10⁻⁵ | 1.338 × 10⁻⁵ | 1.292 |
| 15 | 59 | 1.789 × 10⁻⁵ | 1.470 × 10⁻⁵ | 1.225 |
| 20 | 68 | 1.813 × 10⁻⁵ | 1.516 × 10⁻⁵ | 1.204 |
| 25 | 77 | 1.837 × 10⁻⁵ | 1.562 × 10⁻⁵ | 1.184 |
| 40 | 104 | 1.907 × 10⁻⁵ | 1.702 × 10⁻⁵ | 1.127 |
| 60 | 140 | 1.997 × 10⁻⁵ | 1.896 × 10⁻⁵ | 1.060 |
| 100 | 212 | 2.171 × 10⁻⁵ | 2.306 × 10⁻⁵ | 0.946 |
FAQs
What is the viscosity of air at 20 degrees Celsius?
At 20 °C (68 °F) and standard sea-level pressure, the dynamic viscosity of air is approximately 1.81 × 10⁻⁵ Pa·s (0.0181 mPa·s), and the kinematic viscosity of air is approximately 1.52 × 10⁻⁵ m²/s (15.2 cSt).
What is the viscosity of air at sea level?
At sea level the air pressure is 1013.25 hPa (14.696 psi). At a standard temperature of 15 °C (59 °F), the dynamic viscosity is about 1.79 × 10⁻⁵ Pa·s and the kinematic viscosity is about 1.47 × 10⁻⁵ m²/s. Dynamic viscosity barely changes with pressure, but kinematic viscosity does because it depends on density, which is directly proportional to pressure.
Does air viscosity increase or decrease with temperature?
The dynamic viscosity of air increases with temperature — the opposite of liquids. The kinematic viscosity increases even faster, because the air density drops as the air warms up at constant pressure.
What is the difference between dynamic and kinematic viscosity?
Dynamic viscosity (μ) measures a fluid's internal resistance to shear stress — the force needed to make it flow. Kinematic viscosity (ν) is the dynamic viscosity divided by density (ν = μ / ρ); it describes how quickly the fluid flows under its own inertia. Because air is far less dense than water, its kinematic viscosity is actually higher than that of water, even though its dynamic viscosity is about 50 times smaller.
What does the viscosity of air depend on?
The dynamic viscosity of air depends almost entirely on temperature (through Sutherland's law) and is virtually independent of pressure for everyday conditions. The kinematic viscosity depends on both temperature and pressure, because pressure changes the air density used in ν = μ / ρ.