Know how water your system must add. Include refill intervals, tank size, and rainfall forecasts. Get clear refill counts before you start watering today.
| Scenario | Area | Weekly depth | Interval | Efficiency | Rain | Tank |
|---|---|---|---|---|---|---|
| Raised beds (drip) | 20 m² | 25 mm/week | 7 days | 90% | 5 mm | 60 L |
| Lawn strip (spray) | 500 ft² | 1.25 in/week | 4 days | 70% | 0.20 in | 40 gal |
| Container garden | 8 m² | 35 mm/week | 3 days | 85% | 0 mm | 25 L |
These are example inputs only. Your needs vary by weather, soil, and plant type.
The calculator uses a depth-to-volume approach. First, it converts your weekly water depth to an interval depth, then subtracts effective rainfall, applies mulch reduction, and finally adjusts for system efficiency.
Refill count uses usable tank capacity: Usable = Tank × (1 − Reserve/100).
Refill scheduling protects plants from drought stress while preventing wasted pumping and overflow. This calculator converts a weekly irrigation target into an interval refill volume, so you can match storage to demand and keep watering steady overall during heat spikes.
Consistent refills also reduce pressure swings that can cause uneven coverage across zones.
Area and weekly water depth set the baseline requirement. Interval days turns that target into an actionable refill window. Efficiency accounts for losses from misting, runoff, or poor distribution; drip systems often run 85–95%, while sprays may be 65–80% depending on wind exposure.
Rainfall and effective rain percent reduce demand only when water infiltrates the root zone. A practical effective range is 60–90%, lower on slopes or compacted soils.
IntervalDepth equals (WeeklyDepth ÷ 7) multiplied by Days. EffectiveRain equals Rain times RainEfficiency. The calculator subtracts effective rainfall first, then applies mulch reduction to the remaining need by limiting evaporation and soil heating.
The net depth is divided by system efficiency to estimate gross depth, representing what must leave the tank to achieve desired soil moisture. In metric units, 1 mm over 1 m² equals 1 liter.
When tank capacity is provided, refill count is based on usable storage after a reserve buffer. A 5–10% reserve helps avoid pump starvation and keeps sediment from being stirred up at low levels.
If refills exceed two per interval, consider a larger tank, shorter intervals, or better efficiency through pressure regulation, leak checks, and improved emitter placement.
Update weekly depth as seasons change, especially for new transplants and shallow-rooted beds. Track rain totals per interval, and note storms with high runoff that may contribute little effective water.
Re-check efficiency after filter cleaning, nozzle swaps, or line repairs. Use the per-day volume to set timers, compare zones, and plan refill days around labor and weather forecasts.
It is the estimated volume your tank or reservoir must supply during the selected interval, after subtracting effective rainfall and adjusting for mulch and system efficiency.
Use your local evapotranspiration guidance, crop recommendations, or past irrigation records. For many beds, 20–35 mm/week is common in warm periods, while turf often ranges around 25–40 mm/week depending on climate.
Start with 70–90% for gentle rain on level, mulched soil. Reduce it for short intense storms, slopes, clay compaction, or runoff-prone areas, because less water infiltrates the root zone.
Efficiency represents how much applied water actually reaches roots. If efficiency is 75%, you must supply more water to deliver the same net depth, so gross refill volume rises accordingly.
A 5–10% reserve is a practical starting point. It helps prevent pump cavitation, reduces sediment pickup, and leaves a buffer if your refill day shifts due to weather or labor.
Yes. Run the calculator once per zone using that zone’s area, weekly depth, and efficiency. Add the resulting volumes to estimate total storage needs and to stagger refills across the week.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.