Sprinkler K-factor is based on the following formula:
The real meaning of K-factor is that the flow in gpm can be discharged from the nozzle when the pressure is 1 psi.
While K-factor is used in calculation in other units like that in SI system, the K-factor of a nozzle, such as a sprinkler, a measuring orifice, or even any outlet of a pipe, must be converted to a value based on the units of flow and pressure in such calculation.
The following table offers such conversions:
In Hazen-Williams formula, flow is proportional to pressure to 1.85-th power, and thus K-factor is slightly different from that calculated by the above formula.
In flow testing and sprinkler system calculations using Hazen-Williams formula, K-factor is calculated using the following formula:
A K-factor calculated based on this formula is 45 times of the value calculated based on flow in L/s and pressure in kPa:
If bar is use for SI calculations, K-(L/s-bar) is 1/10 of K-(L/s-kPa), i.e. 4.5.