Watering Schedule Calculator

Inputs

Example Data Table

Examples are illustrative and should be verified with site measurements.

Formula Used

• ET method: weekly depth = reference ET × plant factor × microclimate factor
• Net depth: net weekly depth = max(0, weekly depth − effective rain)
• Per day: depth per watering day = net weekly depth ÷ days per week
• Runtime: minutes = (depth ÷ (app rate × efficiency)) × 60
• Cycles: cycles = ceil(runtime ÷ max cycle minutes)
• Minutes per cycle: runtime ÷ cycles
• US volume: gallons = area(ft²) × depth(in) × 0.623
• Metric volume: liters = area(m²) × depth(mm)

How to Use This Calculator

1. Select units and choose a simple or ET-based method.
2. Enter the irrigated area for your zone or section.
3. Provide target depth or reference ET with factors.
4. Add an effective rain credit for usable rainfall.
5. Enter application rate, efficiency, and days per week.
6. Set cycle/soak limits, start time, and day pattern.
7. Click Calculate to view runtimes and export reports.

Professional Guide to Building a Reliable Watering Schedule

1) Why schedule-based irrigation matters on projects

Watering plans affect plant establishment, turf health, dust control, and client satisfaction. In construction and landscape delivery, consistent scheduling reduces callbacks, prevents stress during hot periods, and supports predictable maintenance. A calculator converts field inputs into run times for crews.

2) Selecting a weekly target depth

A simple approach starts with a weekly depth target, then divides it across watering days. For turf, many plans begin near one inch per week, but the best target depends on soil texture, rooting depth, and season. Increasing days per week shortens each run and can improve infiltration on slopes or compacted subgrade.

3) Using ET-based planning for climate-driven sites

The ET method estimates water need from reference evapotranspiration and adjustment factors. Reference ET represents atmospheric drying demand. Plant factor reflects crop type and maturity, while microclimate factor accounts for wind, shade, and heat near pavement. This method is useful where ET data is available and conditions change weekly.

4) Accounting for effective rainfall

Not all rainfall becomes usable soil moisture. Runoff, interception, and evaporation reduce benefit. Applying an effective rain credit prevents overwatering after storms. In practice, crews often credit only part of reported rainfall.

5) Converting water depth to minutes

Depth alone does not create a schedule; the system’s application rate matters. Application rate (in/hr or mm/hr) describes how quickly sprinklers apply water. Dividing required depth by application rate and irrigation efficiency yields runtime. Measuring application rate with catch cans improves accuracy.

6) Efficiency and distribution uniformity considerations

Irrigation efficiency captures overspray, wind drift, poor overlap, and leaks. Lower efficiency increases required minutes for the same net soil moisture. Improving nozzle selection, pressure regulation, and head spacing can reduce runtime and water use. Documenting assumptions supports clear client reporting.

7) Cycle-and-soak scheduling to reduce runoff

Runoff occurs when application exceeds infiltration capacity. Cycle-and-soak breaks a long runtime into smaller cycles with soak periods between them, allowing water to infiltrate. This strategy is particularly valuable on slopes, clay soils, and freshly graded areas. The calculator estimates cycle count and minutes per cycle from your limits.

8) Producing a practical weekly plan and records

Choose watering days that match site access and local restrictions, then start early morning to reduce evaporation and wind. Keep a consistent pattern and adjust seasonally. Exporting results to CSV or PDF supports approvals, turnover packages, and ongoing maintenance logs for each zone.

FAQs

1) Should I choose the simple method or the ET method?

Use the simple method when you have a known weekly depth target. Use the ET method when you can access local ET data and want schedules that adjust to weather and microclimate.

2) What is a good efficiency value to start with?

Many spray systems perform around 60–75% in real conditions. Start near 70% and refine after checking head spacing, wind exposure, and distribution uniformity using catch-can measurements.

3) How do I measure sprinkler application rate?

Place identical cups across the zone, run irrigation for a set time, then average the collected depth. Convert to an hourly rate. This field test is more reliable than nozzle assumptions.

4) Why does the calculator split runtime into cycles?

If soils cannot absorb water fast enough, long runs cause runoff. Cycle-and-soak uses shorter cycles with breaks to improve infiltration, especially on slopes, clay soils, and compacted areas.

5) What does effective rainfall mean?

Effective rainfall is the portion of rain that becomes usable soil moisture. Some water runs off or evaporates. Crediting only effective rain helps avoid overwatering after storms.

6) Why are early morning start times recommended?

Early morning usually has lower wind and cooler temperatures, reducing evaporation and drift. It also avoids late-day leaf wetness that can contribute to disease on some plantings.

7) Can I use this for multiple irrigation zones?

Yes. Calculate each zone separately because area, application rate, and sun exposure often differ. Save each zone’s results as CSV or PDF to keep clear maintenance and turnover records.