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 together both notations, the K-factor ranges and thread types of NFPA 13-2025 Table 7.2.2.1, the main applications and the minimum pressures, each with its source.
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
The nominal K-factors, K-factor ranges, percentage of K5.6 discharge and thread types are taken directly from NFPA 13-2025 Table 7.2.2.1. The table also lists K1.4 (K20), K1.9 (K27) and K2.8 (K40), which are smaller than K5.6; they are used only in special applications and are omitted below. K57 is not an NFPA nominal value; it is the light hazard (LH) value in EN 12845 Table 37a.
| Metric (L/min/√bar) | US units (gpm/√psi) | K range, metric (NFPA) | Discharge vs K5.6 | Thread type (NFPA) | Main use |
|---|---|---|---|---|---|
| K57 (EN only) | ≈ K4.0 (not an NFPA nominal value) | — | — | — | EN 12845: LH (light hazard) |
| K60 | K4.2 | 57–63 | 75% | ½ in. (15 mm) NPT | NFPA nominal value |
| K80 | K5.6 | 76–84 | 100% | ½ in. (15 mm) NPT | EN 12845: OH, HHP/HHS ceiling (≤ 10 mm/min), in-rack |
| K115 | K8.0 | 107–118 | 140% | ¾ in. (20 mm) or ½ in. (15 mm) NPT | EN 12845: OH, HHP/HHS ceiling, in-rack |
| K160 | K11.2 | 159–166 | 200% | ½ in. (15 mm) or ¾ in. (20 mm) NPT | EN 12845: HHP/HHS ceiling; smallest K for NFPA CMSA (7.2.2.5) |
| K200 | K14.0 | 195–209 | 250% | ¾ in. (20 mm) NPT | ESFR (NFPA Table 23.3.1, EN 12845-2 Table 7) |
| K240 | K16.8 | 231–254 | 300% | ¾ in. (20 mm) NPT | ESFR and CMSA |
| K280 | K19.6 | 272–301 | 350% | 1 in. (25 mm) NPT | NFPA CMSA (Chapter 22); not in the NFPA or EN ESFR tables |
| K320 | K22.4 | 311–343 | 400% | 1 in. (25 mm) NPT | ESFR, ceilings up to 13.7 m |
| K360 | K25.2 | 349–387 | 450% | 1 in. (25 mm) NPT | ESFR and CMSA |
| K400 | K28.0 | 389–430 | 500% | 1 in. (25 mm) NPT | EN 12845-2 ESFR (Table 7, Table 11) |
| K480 | K33.6 | 456–504 | 600% | 1¼ in. (32 mm) NPT | EN 12845-2 ESFR and CMSA; in NFPA, Chapter 24 Table 24.3.3 (dry, standard-response upright) |
Minimum operating pressures
The minimum pressure depends on the hazard class and storage arrangement, not on the K-factor alone. EN 12845 clause 13.4.4 requires, at the most unfavourable sprinkler, the higher of the pressure needed for the density and the following: LH 0.70 bar; OH 0.35 bar; HHP and HHS 0.50 bar; K115 in-rack 1.00 bar; K80 in-rack 2.00 bar.
For ESFR the pressure is read from a table by ceiling and storage height. In NFPA 13-2025 Table 23.3.1 (ceiling-only, pendent) the ranges for Class I–IV and cartoned nonexpanded Group A plastics are as follows; the HHS1–HHS3 rows of EN 12845-2 Table 7 give the same values:
| ESFR K | Minimum pressure range | Source |
|---|---|---|
| K200 (K14.0) | 3.4–5.2 bar (50–75 psi) | NFPA Table 23.3.1; EN 12845-2 Table 7 |
| K240 (K16.8) | 2.4–3.6 bar (35–52 psi) | NFPA Table 23.3.1; EN 12845-2 Table 7 |
| K320 (K22.4) | 1.7–2.8 bar (25–40 psi) | NFPA Table 23.3.1; EN 12845-2 Table 7 |
| K360 (K25.2) | 1.0–2.8 bar (15–40 psi) | NFPA Table 23.3.1; EN 12845-2 Table 7 |
| K400 (K28.0) | 2.8–5.5 bar (15.2–16.8 m ceilings, aisle-width conditions) | EN 12845-2 Table 7 |
| K480 (K33.6) | 3.8 bar (15.2–16.8 m ceilings, aisle-width conditions) | EN 12845-2 Table 7 |
Expanded and exposed plastics need higher pressures: NFPA Table 23.3.1 gives 5.2 bar for K320 and 4.1 bar for K360; EN 12845-2 Table 7 gives 5.2 bar for K320 and 4.1 bar for K360 in HHS4. CMSA pressures are read separately from NFPA Chapter 22 and the EN 12845-2 CMSA tables.
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 Table 37a fixes the permitted nominal K-factors by hazard class: K57 for LH; K80 or K115 for OH; for HHP and HHS ceiling sprinklers K80, K115 or K160 at densities ≤ 10 mm/min and K115 or K160 above 10 mm/min; K80 or K115 for HHS intermediate (in-rack) sprinklers. K200 and above do not appear in this EN 12845 table; ESFR and CMSA are covered by EN 12845-2. Clause 14.2.2 prohibits ceiling, flush, recessed and concealed sprinklers in OH4, HHP and HHS areas; since Table 37a lists these bodies only in the LH and OH rows, the highest K for them under EN 12845 is K115.
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
NFPA 13-2025 Table 7.2.2.1 gives a permitted range for each nominal K-factor; for K80 (K5.6), for example, 76–84 L/min/√bar, roughly −5/+5 percent. EN 12259-1 also defines a tolerance of plus or minus 5 percent on the nominal K value. The nominal value is used in the hydraulic calculation; for dry-type sprinklers NFPA refers to the adjusted K-factor in 28.2.4.10.3. On site the K-factor is identified from the sprinkler's marking (NFPA 7.2.1: manufacturer letters and sprinkler identification number); 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 under EN 12845. Table 37a allows concealed, flush and recessed bodies only in the LH (K57) and OH (K80 or K115) rows, and clause 14.2.2 prohibits them in OH4, HHP and HHS areas.
What is the K-factor tolerance?
EN 12259-1 defines a tolerance of plus or minus 5 percent on the nominal value, and NFPA 13-2025 Table 7.2.2.1 gives a range of the same order for each nominal K (76–84 for K80, for example). The nominal value is used in the calculation.
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Download MEP Calc on the App StoreNFPA 13 (2025) Table 7.2.2.1, 7.2.2.5, Table 23.3.1, Chapter 22 and Table 24.3.3. EN 12845:2015+A2:2026 Table 37a, 13.4.4 and 14.2.2. EN 12845-2:2024 Table 7 and Table 11. EN 12259-1 (sprinkler component standard). EN 12259-13 (ESFR). Manufacturers state a K-factor tolerance of plus or minus 5 percent.