Irrigation Timer Calculator
Calculate sprinkler or drip run time from plant type, system, and soil.
Returns minutes per session and how many cycle-and-soak passes to split it into.
Irrigation timing determines how long to run your watering system to deliver the right amount of water. Too little causes drought stress. Too much wastes water and promotes root rot.
The formula:
Run Time (minutes) = (Water Needed in inches / Application Rate in inches per hour) x 60
Water needs by plant type:
| Plant Type | Inches Per Week | mm Per Week | Used here |
|---|---|---|---|
| Lawn (cool season) | 1.0-1.5 in | 25-38 mm | 1.25 |
| Lawn (warm season) | 0.75-1.25 in | 19-32 mm | 1.0 |
| Flower beds | 1.0-1.5 in | 25-38 mm | 1.25 |
| Vegetable garden | 1.0-1.5 in | 25-38 mm | 1.25 |
| Shrubs (established) | 0.5-1.0 in | 13-25 mm | 0.75 |
| Trees (established) | 0.5-0.75 in | 13-19 mm | 0.6 |
Application rates by system type:
| System | Inches/hour | mm/hour | Used here |
|---|---|---|---|
| Rotary sprinklers | 0.4-0.6 | 10-15 | 0.5 |
| Fixed spray heads | 1.2-2.0 | 30-50 | 1.5 |
| Drip irrigation | 0.5-1.0 | 13-25 | 0.75 |
| Soaker hose | 0.4-0.8 | 10-20 | 0.6 |
Rotors and spray heads differ by roughly three to one, which is the single biggest reason a timer setting that suits one zone drowns or starves another.
Soil changes how you apply the water, not how much
This is the part most irrigation advice gets muddled. A cool-season lawn wants roughly 1.25 inches a week whether it sits on sand or on clay. What changes is whether the soil can take that depth in one pass.
| Soil | Minutes before runoff starts | Holds water | Schedule |
|---|---|---|---|
| Sandy | about 60 | poorly | More sessions, shorter each |
| Loam | about 30 | well | Whatever suits |
| Clay | about 15 | very well | Fewer sessions, split into cycles |
Clay is the one that catches people out. It accepts water slowly, so a 25-minute run mostly ends up on the driveway, and the instinctive fix of running it longer makes that worse rather than better. The answer is cycle and soak: the same total time, broken into short bursts an hour apart, letting each one sink in. Most modern controllers have this built in.
Sandy soil has the opposite problem. Runoff is rarely an issue, but water drains straight past the roots, so a long soak on sand largely waters the subsoil. Little and often wins there.
Best time to water: early morning, 6 to 10 AM. Evening watering leaves foliage wet overnight and invites fungal disease. Midday loses a large share to evaporation before it reaches the soil.
Check your real application rate. The figures above are catalogue averages, and a worn nozzle or low pressure can halve them. Put five straight-sided tins around a zone, run it 15 minutes, measure the depth in each with a ruler, and multiply by four. That gives you inches per hour for your system, on your pressure, and it is usually a surprise.
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This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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