Sprinkler K-Factor Calculator (Flow and Pressure)
The discharge of a sprinkler follows Q = K × √P. Fill in two values and leave the third blank to find flow in GPM, pressure in psi or the K-factor.
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The formulas
- Q = K × √P
- P = (Q ÷ K)²
- K = Q ÷ √P
K is the sprinkler's discharge coefficient. A standard 1/2 in. orifice sprinkler is K 5.6. A sprinkler needs a minimum pressure to operate, commonly 7 psi for standard-response, 7 psi for K 5.6 and higher for large-orifice or ESFR. Check the listing for the actual minimum.
Worked example
A K 5.6 sprinkler at 7 psi flows 5.6 × √7 = 14.8 GPM. At 50 psi the same head flows 39.6 GPM.
Frequently asked questions
What is the usual K-factor?
K 5.6 is the standard 1/2 inch orifice. K 8.0 is a large orifice, and K 11.2 and above are used for extended coverage and storage protection.
What is the minimum pressure?
NFPA 13 sets the minimum design pressure by the sprinkler's listing. A common value for standard spray sprinklers is 7 psi, but extended coverage and ESFR sprinklers have higher minimums.
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This calculator gives an estimate for planning and is not tax, legal or engineering advice. Confirm code-related results against the code edition adopted in your jurisdiction and with your authority having jurisdiction, and follow the manufacturer's instructions.