What Is the Sprinkler Flow Rate Calculator?
This calculator estimates the discharge flow rate of a fire sprinkler or nozzle using the standard hydraulic relationship \(Q = K \times \sqrt{P}\). It is widely used in fire protection engineering, irrigation, and hydraulic design to predict how much water a sprinkler will discharge at a given operating pressure.
How to Use It
Enter the K-factor of your sprinkler head (a discharge coefficient provided by the manufacturer) and the operating pressure in psi at the head. The calculator returns the flow rate in gallons per minute (GPM), along with the equivalent flow per hour. Common K-factors include 5.6 for standard spray sprinklers and 8.0 for large-orifice heads.
The Formula Explained
The governing equation is $$Q = \text{K-Factor} \times \sqrt{\text{Pressure (psi)}}$$ where \(Q\) is the flow rate in GPM, \(K\) is the dimensionless-style discharge coefficient with units of GPM per square root psi, and \(P\) is the pressure in psi. Because flow scales with the square root of pressure, doubling the pressure does not double the flow; it increases it by a factor of about 1.41.
Worked Example
Suppose a sprinkler has a K-factor of 5.6 and operates at 50 psi. Then $$Q = 5.6 \times \sqrt{50} = 5.6 \times 7.0711 = 39.6 \text{ GPM}$$ Over one hour that head discharges about 2,376 gallons.
FAQ
What is a K-factor? It is the nominal discharge coefficient of a sprinkler, set by orifice size and supplied by the manufacturer.
What pressure should I use? Use the residual pressure available at the sprinkler head, not the static supply pressure.
Does this work for irrigation sprinklers? Yes, the same square-root relationship applies as long as you use the manufacturer K-factor and matching pressure units.
