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Full Circular Pipe Flow & Mean Velocity

Relate volumetric flow rate, inside pipe diameter and cross-sectional mean speed for a full circular pipe.

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Enter the known values in the units shown. Results update as you type.
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A 1,000 mm inside-diameter pipe carrying 1 m³/s has mean speed 4/π m/s, approximately 1.27324 m/s.

Mean speed = flow rate / circular area = 4Q / (πd²)

Enter these known values and leave the other values blank.

Inside diameter, flow rate and speed are positive. The pipe cross-section is circular and completely filled.
Use actual volumetric flow at the conditions in the pipe. A standardized gas volume rate needs conversion to actual conditions before applying this area relationship.
This returns average speed, not centerline speed. It does not calculate pressure loss, pump requirements, partial-fill flow or a velocity profile. US and imperial gallons are separate units.

Use the actual inside diameter. Nominal size can differ from inside diameter, and wall thickness affects flow area.

At fixed volumetric flow, doubling diameter quadruples area and reduces mean speed to one quarter.

US gallons per minute use exactly 0.003785411784 cubic meters per gallon and 60 seconds per minute.