Sprinkler hydraulic demand is only part of the water-supply story. Design criteria usually also require a hose stream allowance—extra gpm reserved for firefighter hose lines—so the total demand at the source is sprinkler flow plus hose. This page explains that sketch and gives a free browser calculator: choose a typical educational hose allowance (or enter your own), add sprinkler demand, and see total demand. It is for learning and quick checks—not a substitute for the hose allowance required by your adopted code edition, authority having jurisdiction, or review by a licensed design professional.
How hose stream allowance is used
- Estimate or calculate sprinkler demand for the design area (density × area is a common first pass; full hydraulics will usually be higher).
- Look up the hose stream allowance your project criteria require for the occupancy / hazard (this page does not publish code tables).
- Total demand sketch at the source ≈ sprinkler demand + hose stream allowance (before you layer friction and elevation losses on the supply path).
- Compare that total to available supply (city main, tank, fire pump curve). If supply is short, you revisit density/area, hose value, pump, or tank duration—not just pipe size.
- Do not treat a preset in this calculator as the legal requirement for your job. Confirm the edition and section your AHJ has adopted.
Free calculator
Educational presets only (100 / 250 / 500 gpm are common teaching examples). Override with your project value anytime. Nothing you enter leaves your browser. For density/area sprinkler flow first, see the density/area calculator.
Worked example
Sprinkler demand 300 gpm from a density/area pass, with a 250 gpm hose teaching example: total demand sketch = 550 gpm at the source before pipe friction and elevation. If available supply is entered as 1,000 gpm, the sketch margin is 450 gpm—still not a sealed hydraulic calculation.
Next steps: estimate sprinkler flow with the free density/area calculator, check pipe loss with the Hazen-Williams calculator or the Sprinkler Pipe Friction Loss workbook, and size supply duration with the Fire Pump & Tank Sizing workbook.