Fire Hydrant Flow Test Calculator

Calculate available water supply from fire hydrant flow test using pitot gauge readings and hydrant outlet coefficients

Input Parameters

Results

--
Flow from Hydrant
gpm
--
Total Flow (all outlets)
gpm
--
Residual Pressure
psi
--
Available Flow at 20 psi
gpm
Note: Fire hydrant flow tests per NFPA 291 use pitot gauges to measure velocity pressure at flowing outlets. The discharge coefficient depends on outlet geometry. Results are plotted on N^1.85 graph paper to determine water supply capacity for fire protection design.

Reference

Hydrant Flow Test (Pitot Gauge): Q = 29.84 × Cd × d² × sqrt(P) Q = flow (gpm), Cd = discharge coefficient, d = outlet dia (in), P = pitot (psi) Discharge coefficients: 0.90 (smooth, round), 0.80 (square edge), 0.70 (protruding) Available flow at 20 psi: Q20 = Qt × ((Ps-20)/(Ps-Pr))^(1/1.85)