Flow Rate Calculator

About this calculator

Volumetric flow rate follows the continuity equation Q = A · v — cross-sectional area of the pipe or channel multiplied by the average flow velocity — giving the volume passing a given point per unit time. It's the fundamental relationship behind how fluid engineers size pipes: for a fixed flow rate, a narrower pipe forces a higher velocity, and a wider one slows the flow.

Civil and mechanical engineers use flow rate calculations for plumbing and pipe sizing, HVAC engineers apply it to duct design for adequate airflow, hydrologists use it to describe river and stream discharge, and irrigation engineers size channels and pipes to deliver the right water volume to fields. Enter the cross-sectional area and velocity to find the flow rate.