Hydrant Flow

GPM from Pitot pressure and outlet diameter.

Run the calculator

Example

You enter

Pitot pressure (psi) 10
Outlet diameter (in) 2.5
Coefficient of discharge 0.9

You get

Flow 530 gpm

Details, formula, and sources

Flow GPM = 29.83 × c × d² × sqrt(P_pitot). c = coefficient of discharge (0.90 typical for rounded outlets, 0.80 for square outlets, 0.70 for cocked-back outlets).

AWWA M17 (Installation, Field Testing, and Maintenance of Fire Hydrants) by name; ISO Public Protection Classification fire-flow methodology.

AWWA M17 licensed; principles free at most state-DOT and water-utility training pages.

Estimate. AHJ and licensed fire protection engineer govern.

Field names used by the API: pitot_psi, outlet_diameter_in, c, flow_gpm

Default coefficient 0.90 (rounded outlet) unless user suppliesAWWA M17 typical