Fire Suppression
Sprinkler K-Factor Calculator
Q = K√P. Discharge flow Q (GPM) equals K-factor times the square root of pressure P (psi). Solve for any of the three.
Common K-factors
- K-5.6: standard 1/2" NPT sprinkler — most common in light/ordinary hazard
- K-8.0: standard 3/4" — ordinary/extra hazard
- K-11.2 / K-14: ESFR for warehouse, storage
- K-22.4 / K-25.2: ESFR for very high storage
- K-2.8 to K-4.2: residential and dry-pipe applications
FAQ
Where does the formula come from? +
Orifice flow physics: discharge through an opening is proportional to √(pressure). K = (discharge coefficient × orifice area) constant for that specific sprinkler. Each model has a K-factor on its UL listing.
Minimum pressure required? +
NFPA 13 minimum operating pressure: 7 psi for standard spray (with K-5.6), often 10-15 psi practical minimum. ESFR sprinklers usually require 15+ psi.