Calculate sprinkler flow from pressure, pressure from flow, the K-factor itself, or the pressure needed for a design density, in US (gpm, psi) or metric (L/min, bar) units.
Enter values and click Calculate
The K-factor (discharge coefficient) describes how much water a sprinkler delivers for a given pressure. It depends on the orifice size and shape and is marked on the sprinkler and its listing.
| US K (gpm/√psi) | Metric K (L/min/√bar) | Flow at 7 psi (gpm) | Typical use |
|---|---|---|---|
| 2.8 | 40 | 7.4 | Small spaces, special applications |
| 4.2 | 61 | 11.1 | Residential and small-room sprinklers |
| 5.6 | 81 | 14.8 | Standard ½ in: light and ordinary hazard |
| 8.0 | 115 | 21.2 | Ordinary and extra hazard, extended coverage |
| 11.2 | 161 | 29.6 | Extra hazard, storage, extended coverage |
| 14.0 | 202 | 37.0 | Storage, ESFR and CMSA |
| 16.8 | 242 | 44.4 | Storage, ESFR and CMSA |
| 19.6 | 283 | 51.9 | High-challenge storage, CMSA |
| 22.4 | 323 | 59.3 | ESFR storage |
| 25.2 | 363 | 66.7 | ESFR storage |
| 28.0 | 404 | 74.1 | ESFR storage |
Metric values are exact conversions; manufacturers sell them under rounded names such as K80 (K 5.6), K115 (K 8.0) and K160 (K 11.2). Always use the K-factor from the sprinkler's datasheet.
An ordinary hazard Group 2 area is designed at 0.20 gpm/ft² (8.1 mm/min), with each K 5.6 sprinkler covering 130 ft² (12.1 m²):
Choose "Pressure for a design density" above to repeat this for your own density and spacing. The pressure at the most remote sprinkler is the starting point for the full hydraulic calculation back to the water supply; see Fire Hydraulic Calculator, Sprinkler Density Calculator and the Fire Fighting System Design Calculation guide.
Sizing the pump for the result? See Fire Pump Selection Calculator and Fire Pump Sizing to NFPA 20.
Q = K × √P. Q is the flow, P the pressure at the sprinkler and K the discharge coefficient. Rearranged, P = (Q / K)² and K = Q / √P. In US units Q is in gpm and P in psi; in metric units Q is in L/min and P in bar.
Multiply by about 14.4. K 5.6 (gpm/√psi) is about K 80.7 (L/min/√bar), sold as K80, and K 8.0 is about K 115.
NFPA 13 requires at least 7 psi (0.5 bar) at a standard sprinkler. Some special sprinklers, such as ESFR and extended coverage types, have higher minimum pressures in their listings.
Multiply the design density by the area covered by one sprinkler to get the flow, then use P = (Q / K)². For 0.20 gpm/ft² over 130 ft², Q = 26 gpm, and a K 5.6 sprinkler needs (26 / 5.6)² = 21.6 psi.
A larger K-factor delivers the same flow at a much lower pressure, because pressure falls with the square of K. This reduces the required pump pressure, which is why storage and ESFR sprinklers use K 11.2 to K 28.0.
A standard 1/2 inch orifice sprinkler is K 5.6 (about K 80 metric). It is the most common sprinkler for light and ordinary hazard occupancies.
Found a number that looks wrong, or a case the tool does not cover? Say so here — corrections are welcome and get answered.
No comments yet. Be the first to add one.