Enter the Reynolds number, coefficient of viscosity, the inner diameter of the pipe, and the density of the liquid into the calculator to determine the critical velocity.

Critical Velocity Formula

The following equation is used to calculate the Critical Velocity.

Vc = (R*u) / (D*p) 
  • Where Vc is the critical velocity (m/s)
  • R is the Reynold’s number
  • u is the coefficient of viscosity (m^2/s)
  • D is the inner diameter of the pipe (m)
  • p is the density of the liquid (kg/m^3)

To calculate the critical velocity, multiply the Reynold’s number by the coefficient of viscosity, then divide by the product of the inner diameter and the density.

What is a Critical Velocity?


A critical velocity describes the velocity at which a liquid moving through a tube will turn from laminar flow to turbulent flow.

How to Calculate Critical Velocity?

Example Problem:

The following example outlines the steps and information needed to calculate Critical Velocity

First, determine the Reynold’s number. In this example, the Reynold’s number is found to be 2.5.

Next, determine the coefficient of viscosity. For this problem, the coefficient of viscosity is found to be 30m^2/s.

Next, determine the inner diameter of the pipe. In this case, the inner diameter of the pipe is measured to be .25m.

Next, determine the density of the liquid. For this problem, the density is 1.225 kg/m^3.

Finally, calculate the Critical Velocity using the formula above:

Vc = (R*u) / (D*p)

Vc = (2.5*30) / (.25*1.225)

Vc = 244.89 m/s