Estimate wall shear rate in s⁻¹ for fully developed laminar Newtonian flow in a circular tube, or shear rate between translating parallel plates from relative speed and gap. Optional dynamic viscosity adds shear stress.

Pipe mode assumes fully developed laminar Newtonian flow in a circular tube. Plate mode assumes a linear velocity profile with no slip.

Optional shear stress

Blank omits shear stress. Use viscosity for your fluid, temperature and shear rate.

Related Calculators

Shear Rate Formula

For parallel plates with a linear velocity profile, use SR = V / D. For a circular tube in fully developed laminar Newtonian flow, wall shear rate is SR = 32Q / (πD³), with Q in m³/s and inner diameter D in m.

SR = V / D

Variables:

  • SR is the shear rate (s^-1)
  • V is the relative plate speed (m/s) in the parallel-plates formula
  • D is the gap thickness (m) in the parallel-plates formula

For parallel plates, divide relative speed by gap thickness. For tube flow, select Pipe / tube wall shear rate and enter volumetric flow and inner diameter. Shear rate alone does not determine viscosity; use measured viscosity at the relevant conditions to estimate shear stress as τ = μ × SR.

What is a Shear Rate?

Shear rate is a measure of the rate at which a fluid is sheared or deformed when subjected to a force. It is typically expressed in reciprocal seconds (s^-1) and is the velocity gradient normal to the flow. For a linear parallel-plate profile this is relative speed divided by gap; other geometries require their own formula. This concept is crucial in the study of fluid dynamics and rheology, as it helps determine the viscosity and flow behavior of different fluids under varying conditions. High shear rates can cause some fluids to thin out (shear thinning), while others may thicken or solidify (shear thickening).

How to Calculate Shear Rate?

The following steps outline how to calculate the Shear Rate.

  1. For Parallel plates, determine relative plate speed V and select its unit.
  2. Determine gap thickness D and select its unit. For Pipe / tube, instead enter volumetric flow rate and inner diameter.
  3. Use SR = V / D for parallel plates, or SR = 32Q / (πD³) for pipe flow, after converting to consistent SI units.
  4. Finally, calculate the Shear Rate (SR) in seconds to the power of negative one (s^-1).
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

relative plate speed (V) = 5 m/s

gap thickness (D) = 2 m; shear rate = 5 / 2 = 2.5 s⁻¹