Pipe Flow
How Pipe Diameter Changes Water Flow
See why actual inside diameter strongly affects velocity and pressure loss.
PSI to GPM Editorial Team ·
Pipe diameter affects both available flow area and water velocity. For a fixed GPM, reducing inside diameter raises velocity and usually increases friction loss sharply.
Nominal is not actual
A nominal one-inch pipe does not necessarily have a one-inch opening. Material and schedule determine wall thickness and actual inside diameter.
Check more than one result
Good preliminary sizing checks required diameter, resulting velocity, friction loss, fittings, elevation, and available residual pressure together.