In fire protection engineering, the K-factor formula is used to calculate the discharge rate from a nozzle. Nozzles can be fire sprinklers or water mist nozzles, hose reel nozzles, water monitors and deluge fire system nozzles.

The flow rate of a nozzle is given by, where *q* is the flow rate in litres per minute (LPM), *p* is the pressure at the nozzle in Bar and *K* is the *K-factor* is given in units of .