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Irrigation runtime is the link between water demand in the landscape and the minutes you actually program into a controller. If that link is wrong, plants can stay dry even though the timer runs, or the soil can be pushed past what it can absorb and send water down the slope or into the street.
This calculator turns that planning problem into a controller-ready schedule for either sprinkler or drip irrigation. It can begin with peak-week reference evapotranspiration (ETo) and a crop coefficient, a fixed sprinkler depth per watering event, or a direct weekly gallon target for a drip zone. From there it works out minutes per start, weekly total runtime, gross water applied after losses, and a cycle-and-soak split when the application rate is faster than the soil intake setting.
Everything is calculated in the browser on the page. You supply the weather, rainfall, soil, and system assumptions yourself, then the calculator translates those assumptions into a schedule. It does not pull local weather automatically, inspect sprinkler performance in the field, or check municipal watering restrictions for your address.
Use the result as a planning line for controller setup, then compare it with local conditions, plant response, and any watering limits before treating it as a final schedule.
The calculation has one shared idea and two delivery branches. First, the page estimates how much water the zone needs. Then it increases that requirement to account for efficiency and uniformity losses. Finally, it converts the gross water amount into minutes by using either a sprinkler precipitation rate or a drip zone flow rate.
| Mode | What drives demand | What must be known | What minutes are based on |
|---|---|---|---|
| Sprinkler + ETo | Weekly ETo, crop coefficient, and optional effective rainfall | Precipitation rate, efficiency, uniformity, and watering days or soil-reserve mode | Gross depth per event divided by sprinkler precipitation rate |
| Sprinkler + target depth | A fixed depth per event supplied by the user | Precipitation rate plus the same loss assumptions | Chosen event depth inflated for losses, then converted to minutes |
| Drip + ETo | Weekly ETo, crop coefficient, effective rainfall, and irrigated area | Emitter flow, emitter count or dripline spacing, area, efficiency, and uniformity | Gross gallons per event divided by zone flow |
| Drip + weekly gallons | A fixed weekly gallon goal supplied by the user | Emitter flow, emitter count or dripline spacing, and watering days | Weekly gallons split across starts, then divided by zone flow |
Two advanced controls deserve special attention. Application efficiency and Uniformity (DU) are both entered as percentages, and the calculator multiplies them together. Lower values in either field lengthen the runtime because the same plant demand must be met with a less even or less effective system. This is different from a neutral multiplier model where 1.0 means no change.
The soil-reserve option is available only when demand starts from ETo. In that mode the page uses soil water-holding capacity, active root depth, and management allowable depletion to estimate how many days the root zone can coast between irrigations. It then converts that interval into an effective number of watering days per week. If the sprinkler application rate is faster than the infiltration setting, the same result is split into shorter cycles with soak breaks in between.
Start with the branch that matches the information you already trust. If you have catch-can data or a reliable precipitation rate from an audit, sprinkler mode is the cleanest path. If the zone is built around emitters or inline dripline, choose drip mode and let the schedule be driven by gallons per hour instead of inches per hour.
Use the weather path when the goal is peak-week scheduling. That is the best fit when you have local ETo values, a reasonable crop coefficient, and you want the schedule to move with seasonal demand. Use the fixed-depth sprinkler path when someone has already decided how much water depth should be applied per event. Use the weekly-gallons drip path when you know the total volume the zone should receive but do not want to back into that number from area and ETo.
When the schedule looks surprisingly long, check efficiency, uniformity, and application rate before changing plant demand. Those three assumptions often explain why the gross runtime is much larger than the net water need.
The headline result is the runtime per event multiplied by the effective number of starts per week. In manual mode, that weekly count comes from the watering-days field. In soil-reserve mode, the calculator derives it from root-zone storage and daily demand, so the number of starts can change even when the weekly demand does not.
The summary badges help you see why the answer looks the way it does. The schedule badge tells you whether the result comes from a manual schedule or a soil-reserve interval. The application badge reports either sprinkler precipitation rate, drip application rate when area is known, or drip zone flow when area is not available. If a cycle badge appears, runoff protection is actively splitting the event into smaller pieces.
| If you see this | It usually means | What to check next |
|---|---|---|
| Gross water is much larger than net water | Efficiency and uniformity losses are stretching the schedule | Audit the zone, then revisit the efficiency and DU percentages |
| Two or more cycles appear | Application rate is faster than the soil intake setting | Review precipitation rate, infiltration setting, slope, and soak minutes |
| Average spacing is much longer than field performance suggests | The soil-reserve assumptions may be too generous for the site | Check root depth, allowable depletion, and actual plant stress between sets |
| Runtime drops to zero | Effective rainfall and current ET assumptions cover the week's demand | Confirm the rainfall input and re-check when weather turns hotter or drier |
The tabs below the form answer different planning questions. Controller Plan gives the controller line, seasonal adjustment ladder, and short recommendations. Water Ledger exposes the full metric list and export options. Water Budget Map compares net water, gross water, and soil-reserve capacity in one chart. Cycle/Soak Map turns a split sprinkler event into a time line of running and soaking. The JSON tab captures both the raw inputs and the derived outputs for reuse elsewhere.
One result deserves extra caution: a short sprinkler runtime from a guessed precipitation rate can look more precise than it really is. If the schedule falls into the low single-digit minutes, field measurement matters more than small arithmetic differences.
Default cool-season turf, sprinkler mode. With the built-in cool-season turf preset, 0.22 inches per day of ETo, three watering days per week, and a measured precipitation rate of 1.4 in/hr, the page calculates about 1.23 inches of weekly net demand. After 75% application efficiency and 75% uniformity, that becomes roughly 0.73 inches gross per event, or about 31.3 minutes per start. Because the default infiltration setting is 0.5 in/hr, the event is split into two cycles of about 15.6 minutes each.
Warm-season turf with soil-reserve spacing. Suppose peak-week ETo is 0.18 inches per day, crop coefficient is 0.65, root depth is 8 inches, allowable depletion is 55%, and the precipitation rate is 1.1 in/hr. The root-zone reserve comes out to about 0.73 inches, which supports roughly 6.3 days between irrigations. That translates to an effective schedule of two starts per week. The resulting gross depth is about 0.64 inches per event, which is about 34.9 minutes per start, again split into two cycles when the intake setting stays at 0.5 in/hr.
Direct weekly gallons for a drip zone. Assume a bed needs 48 gallons per week, the controller can water twice per week, and the zone has 20 emitters rated at 1 GPH each. Net demand is 24 gallons per event. After 90% efficiency and 90% uniformity, the gross target rises to about 29.6 gallons per event. With 20 gallons per hour of zone flow, runtime is about 88.9 minutes per start. That is long compared with a sprinkler zone, but it is a normal scale for a modest-flow drip layout.
No. You enter ETo and crop coefficient yourself. The presets provide starting values, but the page does not pull live weather data or location-specific crop factors.
Area is only required when the math has to convert inches of demand into gallons or infer emitter count from dripline spacing. A fixed sprinkler depth can be turned into minutes without area, but ET-based drip scheduling cannot.
It is entered as a percentage of how evenly the zone applies water. Lower uniformity means the driest spots need more total runtime before they catch up, so the page lengthens the schedule by reducing the combined delivery fraction.
That happens when the application rate is higher than the infiltration setting. The page calculates a shorter safe cycle length, then inserts soak breaks so water has more time to enter the soil.
Yes. Drip zones often deliver water slowly on purpose. Long runtimes are common when the total emitter flow is modest, especially in shrub beds and other zones designed for steady soaking rather than spray coverage.
No server-side calculation helper ships with this page. The summary, charts, ledger, and JSON export are generated in the browser after the form values are entered.