The K-factor reduces a sprinkler's discharge performance to a single number. But the same sprinkler is sold as K80 in Europe and K5.6 in America. This page brings both notations, the typical applications and the minimum pressures into one table.
The formula and the unit difference
The underlying relationship is the same in both systems:
Q = K √P
The difference is in the units. EN / metric: Q in litres per minute, P in bar. NFPA / imperial: Q in gpm, P in psi. The conversion factor is approximately 14.4: Kmetric = Kimperial × 14.4.
The full conversion table
| Metric (EN) | Imperial (NFPA) | Nominal orifice | Typical use | Typical min. pressure |
|---|---|---|---|---|
| K57 | K4.2 | 10 mm | LH — light hazard, residential, hotel rooms | 0.7 bar |
| K80 | K5.6 | 1/2" | OH — offices, retail, car parks. The most common head. | 0.35 bar |
| K115 | K8.0 | 17/32" | Heavy OH, HHP, in-rack, excessive clearance | 0.5 bar |
| K160 | K11.2 | 5/8" | HHP/HHS, CMSA, in-rack K11.2 | 0.5 bar |
| K200 | K14.0 | 3/4" | CMSA, ESFR under lower ceilings | 2.4–3.5 bar |
| K240 | K16.8 | — | CMSA, heavy commodities | 3.5–4.0 bar |
| K280 | K19.6 | — | ESFR intermediate class | 3.5 bar |
| K320 | K22.4 | — | ESFR, 10–12 m ceilings | 3.5–4.2 bar |
| K360 | K25.2 | — | ESFR, the high-bay standard | 3.5–5.2 bar |
| K480 | K33.6 | — | ESFR, the tallest stacks | 5.2 bar |
Working out the flow in your head
For a quick metric check: a K80 sprinkler gives 80 L/min at 1 bar. At 4 bar that is 80 × 2 = 160 L/min. Hold those two points and you can verify most site calculations without a calculator.
| K | 1 bar | 2 bar | 3.5 bar | 5.2 bar |
|---|---|---|---|---|
| K57 | 57 L/min | 81 | 107 | 130 |
| K80 | 80 | 113 | 150 | 182 |
| K115 | 115 | 163 | 215 | 262 |
| K160 | 160 | 226 | 299 | 365 |
| K200 | 200 | 283 | 374 | 456 |
| K360 | 360 | 509 | 673 | 821 |
| K480 | 480 | 679 | 898 | 1,095 |
Which K in which hazard class?
EN 12845 fixes the permitted K-factors by hazard class: K57 for LH, K80 or K115 for OH, and K80 through K240 for HHP and HHS. Concealed, flush and recessed bodies cannot in practice go above K115, which makes the architectural choice a hydraulic consequence wherever a high density is required.
The software trap: entering a metric K-factor while the unit set is gpm and psi inflates every flow result by a factor of 14.4. Verify one sprinkler's flow by hand before issuing the calculation.
Tolerance and site checking
EN 12259-1 defines a tolerance of plus or minus 5 percent on the nominal K value. The nominal value is used in the calculation; even if the real nozzle deviates by 5 percent the system stays safe, because the design density is already provided at the most unfavourable sprinkler. On site the K-factor is stamped on the sprinkler body or yoke; the colour code indicates the temperature rating, not the K-factor.
Frequently Asked Questions
Are K80 and K5.6 the same sprinkler?
Yes. K80 is the metric notation (L/min per root bar) and K5.6 the imperial (gpm per root psi). The conversion factor is about 14.4: 5.6 × 14.4 is approximately 80.
How much does a K80 sprinkler deliver at 3.5 bar?
Q = K root P = 80 × root 3.5, about 150 L/min. For a quick check, remember that K80 gives 80 L/min at 1 bar.
What is the highest K-factor in a concealed sprinkler?
K115 in practice. Because concealed, flush and recessed bodies are prohibited in OH4, HHP and HHS anyway, K160 and above are not made in those bodies.
What is the K-factor tolerance?
EN 12259-1 defines a tolerance of plus or minus 5 percent on the nominal value. The nominal value is used in the calculation.
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Download MEP Calc on the App StoreNFPA 13 (2025) sprinkler discharge tables. BS EN 12845:2015+A1:2019 K-factor table. EN 12259-1 (sprinkler component standard). EN 12259-13 (ESFR). Manufacturers state a K-factor tolerance of plus or minus 5 percent.