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Farm Calculators

Irrigation Runtime Calculator

You know how much water one zone should receive and how fast that zone can deliver it. Put those two pieces together to find a run time you can set at the valve or controller.

One active zone

The water target, area and flow must all describe the same zone.

Changing units converts valid entries.

1. Set the water target

Use the amount planned for this zone, not the whole field.

Choose the form in which your plan gives water.

Gross already includes losses; net needs an efficiency estimate.

mm

Enter 0 if this zone needs no water now.

ha

Exclude areas served by other zones.

2. Enter flow while this zone runs

Only the outlets open in this zone count.

L/min

The total flow of this zone while it is open.

Optional identical zones

Default 1. Use more only when each zone has this same target and flow, and runs one after another.

Time at the valve

This is the time for one zone with the entered target and active flow.

Run time per zone

Enter a water target and active zone flow, then calculate.

Runtime is an estimate from the entered target and flow. Check actual pressure, distribution, soil intake and runoff before copying the time into a controller. Different zones need separate calculations when their areas or flow differ.

From water target to timer setting

One zone, one water target, one run time

You are ready to open a valve, but the plan gives water in millimetres or gallons—not minutes. The missing piece is the flow of the outlets that will run together.

Give this calculator the water planned for one active zone and that zone’s flow. It turns the plan into an operating time. If the next zone has a different area or different outlets, calculate it separately.

How to use the calculator

Step 1

Match the target to one zone

Choose a depth and enter the area served by this zone, or enter a volume already planned for it. Select Water to deliver (gross) if losses are already included. If the target is water needed at the roots, select Water needed at roots (net) and enter application efficiency.

Step 2

Describe the outlets that are open

Use measured total zone flow when you have it. For drip, enter active emitter count and one emitter’s hourly flow. For sprinklers, enter active head count and flow per head. Use values at the pressure at which the zone actually operates.

Step 3

Set the time, then watch the first run

The main result is the run time for this zone. Open Optional identical zones only if other zones have the same target and flow; the total assumes they run one after another. Before repeating the setting, check the soil and coverage during a real run.

How the calculation works

Think of it as filling a measured container: run time = water to deliver ÷ active zone flow. The water and flow must use the same volume unit, and flow must be per minute to give minutes.

Depth target: 1 mm over 1 ha = 10,000 L; 1 inch over 1 acre = 27,154.2857 US gal.

Net target: water to deliver = root-zone target ÷ (efficiency ÷ 100). A gross target skips this step.

Active flow: measured flow, or emitters × hourly emitter flow ÷ 60, or sprinkler heads × flow per head.

The calculation keeps full precision. The clock guide rounds to the nearest second and shows “<1 sec” for a tiny positive time rather than calling it zero. A controller setting may need a small practical adjustment.

Three ways a zone's flow may be known

Measured flow

Depth across a field block

A 10 mm gross target over 0.5 ha is 50,000 L. At 1,000 L/min, run that zone for 50 minutes. Three identical zones take 150 minutes sequentially.

Drip emitters

Water at the roots

Five millimetres over 0.01 ha is 500 L net. At 80% efficiency, deliver 625 L. One hundred emitters at 2 L/h supply 3.3333 L/min, so run the zone for 187.5 minutes.

Sprinkler heads

A known volume

Four heads at 5 US gal/min each give 20 US gal/min. To deliver 600 US gal gross, run the zone for 30 minutes. Check the pattern in the field; head flow alone does not prove even coverage.

Net and gross: count losses once

“Net” is the water intended to stay useful in the root zone. “Gross” is the water the system must deliver to account for the efficiency you entered. If a water plan already gives gross depth or gross volume, use the gross option here.

For example, a 600 US gal net target at 75% efficiency requires 800 US gal through the zone. At 20 US gal/min, that is 40 minutes. Entering the same 800 gal as gross also gives 40 minutes—do not divide it by 75% again.

Coming from Crop Water Requirement? Use its gross application depth or gross volume with the gross option. Its net depth belongs with the net option and the same efficiency used in that water plan.

Why the zone boundary matters

A hectare-wide target paired with the flow from one small corner will create a very long time. That is a mismatch, not a mysterious result. Measure only the area supplied by the outlets open together.

The identical-zones option is deliberately narrow. It multiplies one-zone time and water by the count, assuming one valve opens after another. It does not compare different zones or create start times for an automatic controller.

Before you copy minutes into the controller

  • Check flow while the zone runs. A pump or head rating at another pressure may not match field flow.
  • Look for dry and wet patches. Equal total flow does not mean every emitter or sprinkler covers evenly.
  • Watch the soil. If water ponds or runs off, one long cycle may not be suitable even when the arithmetic is correct.
  • Recalculate changed zones. A valve repair, clogged filter, extra lateral or different water target changes the time.

The calculator does not decide the crop’s water need, irrigation frequency, infiltration limit or pressure losses. Use a field plan and current conditions to choose the target first.

Frequently asked questions

Should my water target be net or gross?
Choose gross delivery if your planned depth or volume already includes system losses. Choose net root-zone need if the target describes water the crop should receive; then enter application efficiency so the calculator can estimate how much water must pass through the zone.
Can I use the result from Crop Water Requirement Calculator?
Yes. Use its gross application depth or gross volume with Gross delivery here, and use the same zone area. Or use its net irrigation depth with Net root-zone need here and the same efficiency. Do not divide a gross result by efficiency again.
Which flow should I enter for drip irrigation?
Use the number of emitters actually operating in this one zone and the rated flow of one emitter at its operating pressure. The calculator converts their combined hourly flow to flow per minute.
Can I use a sprinkler catch-can rate instead of head flow?
The sprinkler mode uses head count and flow per head. A measured catch-can precipitation rate is a different method: divide a compatible target depth by that measured rate, taking care not to apply efficiency twice.
What does the identical-zones option assume?
Every zone has the same water target, area when depth is used, and active flow. Total sequential time assumes one zone runs after another. Calculate zones separately when their areas, emitters, heads or flow differ.
Does zero minutes mean the irrigation system is broken?
No. A zero water target produces a zero-minute result. It means this entry calls for no water; it does not diagnose the system or decide when irrigation is needed next.
Is this a complete irrigation schedule?
No. The result is arithmetic operating time for the entered target and flow. Soil intake, pressure, runoff, uniformity, weather and crop conditions can require adjustments or multiple shorter cycles.