# Reynolds Number Calculator

The Reynolds number is an important dimensionless quantity used to predict whether a flow is laminar or turbulent,
and is defined as the **ratio of inertial to viscous forces in a fluid**.

The calculator can either be used in manual mode (density, viscosity or kinematic viscosity known); or alternatively use it in conjunction with the built-in Standard Atmosphere calculator to quickly determine the Reynolds number in a standard atmosphere for any altitude and temperature combination.