Reynolds number calculator
The Reynolds number is the ratio of inertial to viscous forces, and it decides whether a flow is orderly or chaotic.
kg/m3
Pa s
Water at 20 C: 0.001002. Air: 1.81e-5. SAE 30 oil: about 0.2.
Reynolds number
99 600.798
- Kinematic viscosity
- 0.000 001 004 01 m2/s
- Velocity at which it turns transitional
- 0.046 184 4
Show the working
- Velocity = 2
- Characteristic length = 0.05
- Density = 998
- Dynamic viscosity = 0.001 002
- Reynolds number = 998 * 2 * 0.05 / 0.001 002 = 99 600.8
- Kinematic viscosity = 0.001 002 / 998 = 0.000 001 004 01
- Velocity at which it turns transitional = 0.05 > 0 ? 2300 * 0.001 002 / (998 * 0.05) : 0 = 0.046 184 4
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- Re = rho v D / mu = v D / nu
The 2300 and 4000 thresholds apply to flow in a circular pipe. External flows over plates and spheres transition at very different numbers.