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NFPA 13
Validated against the standard.
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How it works
Enter your values
Type in your inputs — the app fills code tables and constants for you, so there's nothing to look up.
Get a code-checked result
Instant answer with a clear PASS / FAIL and the exact NFPA 13 reference behind every number.
Save & export
Keep a history of calculations and export a clean PDF report to share or attach to a permit (Pro).
What this calculator does
Sprinkler hydraulic calculations prove that a system can deliver the required water density over the design area. This app runs the NFPA 13 density/area method with the sprinkler discharge equation and Hazen-Williams pipe friction, so you can balance a system and compare demand to the available supply.
The core equations
Q = K √P — sprinkler discharge, where K is the orifice K-factor (5.6 for a standard 1/2-inch head) and P is pressure in psi.
Pipe friction uses the Hazen-Williams formula with a C-factor for the pipe material, summed node by node from the most remote head back to the source.
Worked example
A K-5.6 head at 7 psi flows Q = 5.6 × √7 = 14.8 GPM. The app then adds friction back through the branch and cross-mains to find the total demand and required pressure at the base of the riser.
Related calculators
Set the design density with the hazard classification calculator and confirm the source with the water supply calculator.
Sprinkler hydraulic FAQ
What is the density/area method?
NFPA 13 sets a required water density (gpm per square foot) over a design area based on the occupancy hazard. The system must supply that density over the most demanding area.
What is a K-factor?
The K-factor relates a sprinkler's flow to pressure through Q = K√P. A standard 1/2-inch orifice head has K = 5.6; larger-orifice heads have higher K-factors.
What pipe friction model is used?
The Hazen-Williams equation with a C-factor for the pipe material, the method NFPA 13 specifies for sprinkler hydraulic calculations.
Does it work offline?
Yes, it runs 100% offline with no account. Free with rewarded ads; a one-time $2.99 Pro unlock adds PDF export and saved history.
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