FLUID VELOCITY INSIDE PIPE Pipe Flow Velocity Calculator Calculate the average velocity v from volumetric flow rate Q and internal diameter D with v = Q / A and A = π·D²/4. Flow rate (Q) m³/s m³/h L/s L/min Comma or dot accepted. Input method for internal diameter (D) Direct value DN + Schedule Internal diameter (D) m cm mm in Use the internal pipe diameter. Nominal Diameter (DN) Schedule 5S 10S 40 80 Calculated internal diameter (mm) Calculate Reset Result — m/s Average velocity in pipe