Sprinkler Head Flow Rate Calculator
Calculate the flow rate through a sprinkler head using the K-factor formula. Enter the K-factor and pressure to determine the discharge flow rate.
Common values: 2.8, 4.2, 5.6, 8.0, 11.2, 14.0, 16.8, 19.6, 22.4, 25.2
Formula
Q = K × √P
- Q = Flow rate (US gallons per minute, gpm)
- K = K-factor of the sprinkler head (gpm / psi½)
- P = Pressure at the sprinkler head (psi)
Unit Conversions used:
- 1 bar = 14.5038 psi
- 1 kPa = 0.145038 psi
- 1 gpm = 3.78541 L/min
- 1 gpm = 0.227125 m³/h
Example: A K-5.6 sprinkler at 7 psi: Q = 5.6 × √7 = 5.6 × 2.646 = 14.82 gpm
Assumptions & References
- The K-factor formula Q = K√P is defined in NFPA 13 (Standard for the Installation of Sprinkler Systems) and FM Global Property Loss Prevention Data Sheets.
- K-factor values are stamped or listed on listed sprinkler heads per UL 199 / UL 1767 listings.
- Pressure must be in psi and flow in gpm for the standard K-factor formula; metric K-factors use bar and L/min (Kmetric = Kimperial × 14.4).
- Minimum operating pressure for standard spray sprinklers is typically 7 psi (0.48 bar) per NFPA 13 §8.2.1.
- Maximum pressure at any sprinkler is typically 175 psi (12.1 bar) per NFPA 13 §8.2.2.
- Common K-factors: K-2.8 (residential), K-5.6 (standard), K-8.0 (large orifice), K-11.2 (extra large), K-14.0, K-16.8, K-19.6, K-22.4, K-25.2 (ESFR).
- This calculator assumes a single sprinkler head. Hydraulic calculations for full systems must account for pipe friction losses (Hazen-Williams) and demand areas per NFPA 13.
- Results are for estimation purposes. Always verify with a licensed fire protection engineer for system design.