Sprinkler Flow Calculator (K-Factor)
Calculate single-head fire sprinkler discharge flow from listed sprinkler K-factor and operating pressure.
- Enter the sprinkler K-factor Input the listed K-factor from the sprinkler data sheet or nameplate (for example 5.6 for many light-hazard heads).
- Enter operating pressure Type the pressure at the sprinkler outlet in psi, not the pump header pressure.
- Run the discharge calculation Press Calculate to compute flow rate in GPM using Q = K × √P, with a metric L/min conversion.
How do you calculate sprinkler flow from K-factor?
Use the standard discharge equation Q = K × √P, where Q is GPM, K is the sprinkler orifice coefficient, and P is pressure at the sprinkler in psi. For example, K = 5.6 at 7 psi yields about 14.8 GPM. The calculator performs that same equation directly.
Can I use pump pressure instead of sprinkler pressure?
No. Use pressure at the sprinkler outlet after accounting for elevation and friction losses through the piping network. Pump discharge pressure is upstream and can overstate actual sprinkler discharge if losses are not removed.
Is single-head flow enough to size a system?
No. System demand requires remote-area calculations including multiple operating sprinklers, fitting losses, elevation effects, and hose allowance per applicable standards. This calculator is a quick single-head pre-check only.
How much flow does a K-5.6 sprinkler need at 7 psi?
Using Q = K x sqrt(P), a K-5.6 sprinkler at 7 psi discharges about 14.8 GPM. That value is a common quick-check benchmark for light-hazard examples. Final design still depends on the listed sprinkler and full system hydraulic calculation.
Can I back-calculate pressure from required sprinkler GPM?
Yes. Rearranging the discharge equation gives P = (Q / K)^2, so you can estimate outlet pressure needed for a target flow. Use the listed sprinkler K-factor and remember this is at the sprinkler outlet, not pump discharge.
Does this include hose allowance or remote area calculations?
No. This calculator evaluates one sprinkler head only and does not include hose stream allowance, remote-area density/area method requirements, or full network hydraulic balancing. Treat it as a first-pass check before complete code-compliant demand calculations.
What happens if pressure doubles at the sprinkler?
Flow increases by the square root relationship, not linearly. Doubling pressure increases discharge by about 41%, because Q is proportional to sqrt(P). This is why pressure gains produce diminishing flow gains at the sprinkler orifice.