Calculator
Formula used
Net = max(0, ETo x Kc - Pe)
Adjusted = Net / (1 - LF)
Gross = Adjusted / Efficiency
Because 1 mm over 1 m2 equals 1 liter:
Daily liters = Gross(mm/day) x Area(m2)
Daily m3 = Daily liters / 1000
This calculator estimates planning volumes for irrigation demand. For detailed design, consider soil intake rate, emitter flow, zoning, and local water quality constraints.
How to use
- Enter the irrigated area and choose the correct unit.
- Add your local ETo and select a suitable Kc value.
- If relevant, input effective rainfall to reduce the net requirement.
- Set irrigation efficiency based on your system and site losses.
- Use leaching fraction only when salinity management is needed.
- Choose the planning period and number of irrigations, then calculate and export.
Example data table
| Scenario | Area (m2) | ETo (mm/day) | Kc | Rain (mm/day) | Efficiency (%) | Days | Daily (m3/day) | Total (m3) |
|---|---|---|---|---|---|---|---|---|
| Site turf zone | 500 | 5.2 | 0.85 | 0.0 | 75 | 30 | 2.947 | 88.410 |
| Shrub bed | 250 | 4.6 | 0.65 | 0.3 | 70 | 21 | 0.992 | 20.832 |
| High-salinity site (LF 10%) | 800 | 6.0 | 0.80 | 0.0 | 78 | 14 | 4.379 | 61.306 |
Example values are illustrative. Use local climate data for best accuracy.
Water planning for active work areas
Construction sites often need temporary irrigation for turf establishment, erosion control, dust suppression, and landscape handover. This calculator converts climate demand into deliverable volumes, so you can size storage tanks, bowser refills, or temporary mains. In many warm regions, daily ETo commonly falls between 3 and 7 mm/day, which can translate into several cubic meters per day even on modest areas during early establishment and handover.
Key inputs and what they represent
ETo is the local reference evapotranspiration; Kc scales that value for the surface you are watering. Typical Kc ranges include 0.70–0.90 for maintained turf and 0.50–0.70 for shrub beds. Effective rainfall (Pe) reduces the net demand and should reflect what actually infiltrates and is stored, not the full rainfall total. Shade, mulch, and seasonal dormancy can lower real demand, so adjust Kc conservatively.
Losses, efficiency, and leaching allowance
Efficiency accounts for losses from wind drift, uneven distribution, leakage, and runoff. Temporary hose and sprinkler setups may operate around 60–75%, while well-designed systems may reach 75–90%. Leaching fraction adds a controlled extra percentage where salinity management is required; values of 5–15% are common when water quality or soil salts justify it. Pressure regulation and nozzle wear strongly influence distribution uniformity over time.
Turning daily demand into a workable schedule
The period and irrigations-per-period fields translate daily volume into event volume for tanker trips, pump runtime, or night watering windows. If your site has flow limits, increase the number of events to reduce peak demand per event, while keeping the same total volume for the period. Add a buffer for weekends, access restrictions, and heat spikes.
Quality checks before relying on results
Confirm units, then validate output with a quick field test: run the system for a timed interval and measure catch-can depth. Compare measured mm/hr to the planned requirement and adjust efficiency or scheduling. Always consider infiltration rate, slope, and zoning to prevent runoff and overspray onto fresh concrete, excavations, or electrical works.
FAQs
What if I do not know local ETo?
Use a nearby station value or a design-month estimate. If uncertain, run low and high cases, such as 4 and 6 mm/day, to bracket storage, deliveries, and budget.
Should I enter total rainfall or effective rainfall?
Enter effective rainfall only. It is the portion that infiltrates and remains available. Intense storms may be less effective due to runoff or drainage beyond the root zone.
How do I choose irrigation efficiency?
Start at 70% for temporary sprinklers and 75–85% for managed systems. Adjust after a catch-can test. If wind drift, leaks, or runoff occur, use a lower efficiency.
Why does leaching fraction increase the requirement?
Leaching adds extra water to flush salts below the root zone. It increases gross depth because the added volume is intentional and still passes through the same distribution losses.
Can I use this for dust suppression water?
Yes, as a planning baseline, but dust control is operational and may exceed evapotranspiration needs. Treat the calculated volume as a minimum, then add allowances for traffic and wind.
How is cost calculated?
Cost equals total volume (m3) multiplied by your unit rate per cubic meter. If charges are per tanker or per hour, convert them into an equivalent per-m3 rate for comparison.