Sprinkler discharge · Q = K√P · fire protection reference
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Common K-Factors (Quick Select)
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Flow vs Pressure Curve
This table lists K-factors commonly associated with standard sprinkler orifice designations. Actual K-factors vary by manufacturer and model. Always verify from the specific sprinkler datasheet.
| K-Factor | Nominal Orifice | Thread Size | Type | Typical Use |
|---|
This K-factor calculator is a quick-reference tool for fire protection engineers, designers, contractors, and students working with automatic sprinkler systems. It uses the standard hydraulic discharge equation Q = K√P to relate flow rate, pressure, and the sprinkler's K-factor.
The calculator can solve for any one of the three variables when the other two are known, and includes a multi-head multiplier for rough total flow estimates when heads operate at equal pressure.
This calculator assumes steady-state conditions with static K-factors. Real sprinkler systems involve friction loss, elevation changes, and varying pressures across heads. Use hydraulic calculation software for design-level work. The multi-head multiplier assumes equal pressure at every sprinkler, which does not occur in practice.
All three modes rearrange the same fundamental sprinkler discharge equation.
Where Q = flow rate (GPM), K = discharge coefficient (GPM/√PSI), and P = pressure (PSI).
The K-factor is a dimensionless-in-practice discharge coefficient that characterizes how much water a sprinkler orifice will deliver at a given pressure. Higher K-factors deliver more water at the same pressure. K-factors are established through laboratory testing and are listed on each sprinkler's UL/FM datasheet.
When selecting sprinklers for a project, the K-factor affects system demand, pipe sizing, water supply requirements, and pump selection. Designers should not assume a K-factor based on orifice size alone — always verify from the manufacturer's published data.
K-factor is a sprinkler's discharge coefficient. It describes the relationship between pressure at the sprinkler and the flow rate it produces. A higher K-factor means more flow at the same pressure.
K-5.6 is the most widely used K-factor for standard spray sprinklers in commercial and light hazard occupancies. K-8.0 and K-11.2 are also very common for higher-flow applications.
The Q = K√P formula applies to all sprinklers including ESFR, but ESFR design involves additional requirements (minimum pressures, ceiling clearances, storage configurations) that this calculator does not address. Use it for quick flow checks, not ESFR system design.
It is a simplification for rough estimates. In a real piped system, pressure varies at each sprinkler due to friction loss and elevation differences. Accurate multi-head calculations require hydraulic analysis software.
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