The Froude number is a dimensionless number used in fluid mechanics and naval architecture to characterize the relative importance of inertia forces compared to gravitational forces. It’s named after William Froude, a British engineer who introduced it in the 19th century.

Froude number is proportional to { (inertial force) / (gravitational force) } and is used in momentum transfer in general and open channel flow and wave and surface behavior calculations in particular. It is normally defined in one of the following forms