What is the Reynolds Number and how can we calculate it?

The performance of flowmeters can be affected by a dimensionless unit called the Reynolds Number. It is defined as the ratio of the liquid's inertial forces to its drag forces.


Laminar and turbulent flow are most common in flow regimes or in liquid flow measurement operations but there is also transitional flow.

If we want to calculate the Reynolds number , we can use the following equation

R = 3160 x Q x Gt D x µ

where: R = Reynolds number
Q = liquid's flow rate, gpm
Gt = liquid's specific gravity
D = inside pipe diameter, in.
µ = liquid's viscosity, cp

When the Reynolds number is greater than 4000, flow will be described as turbulent
When the Reynolds number is in the range of 2000 to 4000 the flow is considered transitional.
Viscosity can be a major factor that affects the value of the Reynolds number.

For e.g You may find highly viscous hydraulic oils may exhibit laminar flow in most conditions while things like water will be turbulent