🚒 Fire Flow Calculator
Estimate the needed fire flow (in gallons per minute) for a building using the standard ISO fire flow formula.
What is Needed Fire Flow?
Needed Fire Flow (NFF) is the estimated rate of water supply, in gallons per minute, that firefighters would need to control a fire of a given size in a given building. It’s widely used in fire protection engineering and water system planning.
The ISO Formula
This calculator uses the Insurance Services Office (ISO) formula: NFF = 18 × C × √A, where A is the total floor area in square feet (floor area per story × number of stories) and C is a coefficient based on construction type — fire resistive (0.6), noncombustible (0.8), ordinary or heavy timber (1.0), and wood frame (1.5). The result is rounded to the nearest 250 gpm and bounded between 500 and 12,000 gpm, matching common ISO practice.
Real fire flow requirements also depend on exposures from nearby buildings, occupancy hazard, and local fire code — this calculator gives a general planning estimate only and is not a substitute for a professional fire protection engineering assessment.