Scheduling Coefficient Calculator

For turf and landscape sprinkler systems: figures out how much longer a system needs to run than a "perfectly uniform" system would, so that the driest 25% of the lawn still gets adequately watered. The everyday question this answers: "my controller says 20 minutes per zone — is that actually enough?"

Calculator

Distribution uniformity (DU)

From a catch-can test — see the Catch-Can Uniformity Calculator.

Solve for

Actual run time needed Run time if uniformity were perfect

Run time if uniformity were perfect

This is simply desired depth ÷ application rate — e.g. 0.5 in at 0.25 in/hr = 2 hr.

Actual run time

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About this calculator

The scheduling coefficient (SC) is simply the inverse of DU. If DU = 0.80, SC = 1.25 — the system needs to run 25% longer than a perfectly uniform system would, so that the driest spots (the low quarter) still receive the target depth.

d_LQ = DU × d_z — SC = d_z / d_LQ = 1 / DU — actual time = ideal time × SC

Textbook Example 5.4: A sod farm system has DU=0.80, d_z=1.5 in, and ran for 5 h. SC = 1/0.80 = 1.25, d_LQ=1.2 in. With perfect uniformity, the same result would have taken 5 h ÷ 1.25 = 4 h. Click "Load textbook Example 5.4" above (solving for the perfect-uniformity time) to see it worked through.