Reynolds Number Calculator

About this calculator

This calculator computes the Reynolds number, Re = ρvL/μ, a dimensionless ratio of inertial to viscous forces in a fluid. Enter the fluid's density, velocity, a characteristic length (like pipe diameter), and viscosity to get Re, plus whether the flow is laminar, transitional, or turbulent.

Mechanical and civil engineers rely on it to design pipelines, HVAC ducts, and aircraft wings, since the flow regime changes drag, heat transfer, and mixing behavior dramatically. It is one of the first numbers checked in any fluid mechanics problem.