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Irrigation runtime calculator

What the turf used, what the rain gave back, and how long your system takes to make up the difference.

Precipitation rate
Runtime
41 min
Precipitation rate
4.3 mm/h
Water used (ETc)
2.6 mm
Net to put back
2 mm
Gross, allowing for uniformity
2.9 mm

A guide, not a schedule. Wind, slope, soil and a blocked nozzle all change what reaches the turf. A catch-can test on your own system beats any spacing calculation.

How it’s worked out

  • Water used: ETc = ET₀ × Kc. The Kc defaults are set per surface (see below); change them to yours.
  • Net depth: ETc × % to put back − rain, never below zero.
  • Gross depth: net ÷ DU, using the lower-quarter distribution uniformity so the driest quarter still gets the net depth.
  • Precipitation rate from spacing: flow L/min × 60 ÷ area per head — spacing × spacing for square, × 0.866 for triangular. One litre on one square metre is exactly one millimetre.
  • Runtime: gross ÷ rate × 60 minutes, split into cycle-soak passes when one pass would be deeper than the surface takes in.

Where the maths comes from

  • Greens Kc 0.85 is the FAO-56 cool-season turf figure less the 0.10 FAO allows for careful water management. Tees 0.8 is the University of California annual cool-season figure. Fairway 0.75 and rough 0.6 are set deliberately lean; published cool-season figures run from about 0.76 upwards.
  • Net depth is crop use less effective rain, then grossed up for losses: the order in the FAO irrigation water management manual. FAO grosses up by irrigation efficiency; this calculator uses lower-quarter DU in its place, as the University of California turf guide does.
  • Precipitation rate and the 0.866 triangular factor: Toro’s published sprinkler formulas, converted to litres and metres.
  • The most a single pass puts down before it splits into cycle-soak passes is a cautious TurfWise default per surface, not a published figure. A sand-based green takes water much faster than its 6 mm default, so on free-draining greens treat the extra passes as cautious rather than necessary.

On Premium, TurfWise’s irrigation module works from your own heads, pressures and flows. Start free — the daily loop is free for one course.