K Factor Calculator

GPM
PSI
in
in
Construction

Calculate the K-factor for fire sprinklers (K = Q / √P) or sheet metal bending K-factor.

Formula

Sprinkler: K = Q / √P; Sheet metal: K = neutral axis offset / material thickness
  • Sprinkler: Q (GPM), P (PSI). Typical K values: K2.8 (residential), K5.6, K8, K11.2 (commercial).
  • Sheet metal: K ≈ 0.3 (sharp bend, soft metal) to 0.5 (large radius, hard metal).
  • NFPA 13 lists standard K-factors. Always verify with the sprinkler manufacturer's data sheet.

Fire sprinkler: Q=20 GPM, P=10 PSI

Inputs
  • Application: sprinkler
  • Flow Rate Q: 20 GPM
  • Pressure P: 10 PSI
  • Neutral Axis Offset: 0.1 in
  • Material Thickness: 0.125 in

K = 20 / √10 = 20 / 3.162 = 6.32 (approximately K5.6 or K8 standard size)

Frequently asked questions

What does K-factor mean for a sprinkler?
K-factor characterises the flow rate at a given pressure. A higher K-factor means more water at the same pressure. Standard K5.6 produces ~13 GPM at 5.2 PSI.