| Soil | Root depth (m) | ET0 (mm/day) | Kc | Rain (mm/day) | Eff. | Rate (mm/hr) | Interval (days) | Gross depth (mm) | Runtime (min) |
|---|---|---|---|---|---|---|---|---|---|
| Loam | 0.25 | 5.5 | 0.85 | 0.5 | 0.75 | 15 | 3.6 | 12.5 | 50 |
| Sandy loam | 0.35 | 6.2 | 0.80 | 0.0 | 0.90 | 10 | 3.3 | 17.1 | 103 |
| Clay loam | 0.45 | 4.8 | 0.90 | 1.0 | 0.75 | 12 | 7.5 | 43.2 | 216 |
- ETc = ET0 × Kc (unless ETc is overridden).
- NetDailyUse = max(ETc − EffectiveRain, 0).
- TAW = AWC × RootDepth (mm).
- RAW = TAW × p (mm), where p is allowed depletion.
- Interval = RAW ÷ NetDailyUse (days).
- GrossDepth = RAW ÷ Efficiency (mm).
- Runtime = GrossDepth ÷ ApplicationRate (hours).
- Volume(L) = Area(m²) × GrossDepth(mm).
- Pick a soil type, then set root depth and allowed depletion.
- Enter ET0 and Kc, or directly enter ETc.
- Add average effective rainfall if you expect regular rain.
- Select a system type, then verify efficiency and rate.
- Press Calculate to view the recommended interval and runtime.
- Use CSV/PDF downloads to share schedules with crews.
Construction landscapes face compaction, grading, and sparse cover, so water demand shifts quickly. This calculator turns weather demand and soil storage into a repeatable irrigation interval. Run one zone per calculation for consistent decisions. Use the safety interval when access is limited.
The root zone is a reservoir. Total available water is AWC × root depth, and allowed depletion sets the usable portion. Typical planning AWC values range from 60–110 mm/m for sands to 150–180 mm/m for loams and silts. Verify root depth after backfill and settlement on active sites.
If ETc is not entered, ETc is calculated as ET0 × Kc. For turf, Kc commonly ranges 0.75–0.95. Effective rainfall should reflect infiltration after runoff and drainage; on compacted slopes it can be near zero.
Interval controls how often to irrigate, while gross depth and runtime control how much to apply each cycle. Efficiency accounts for uniformity and losses; planning values often use 0.75 for sprinklers and 0.90 for drip. Measure application rate with catch-cans so runtime matches reality.
Example: AWC 150 mm/m, root depth 0.25 m, and p 0.50 gives RAW 18.75 mm. With ET0 5.5 mm/day and Kc 0.85, ETc is 4.68 mm/day; with 0.5 mm/day effective rain, net use is 4.18 mm/day and interval is about 4.5 days. At 0.75 efficiency, gross depth is 25.0 mm; at 15 mm/hr, runtime is about 100 minutes.
| Soil | Root depth (m) | ET0 (mm/day) | Kc | Interval (days) | Runtime (min) |
|---|---|---|---|---|---|
| Loam | 0.25 | 5.5 | 0.85 | 4.5 | 100 |
1) What does “allowed depletion” mean?
Allowed depletion (p) is the fraction of stored root-zone water you let plants use before irrigating. Lower values reduce stress but increase watering frequency and operational visits.
2) Should I enter ETc or ET0 and Kc?
Use ETc if you already have zone-specific water use from a trusted source. Otherwise, enter ET0 and Kc so the calculator derives ETc consistently across zones.
3) How do I estimate effective rainfall on a site?
Start with measured rainfall, then subtract runoff and drainage losses. On compacted or sloped areas, effective rainfall can be minimal. Use conservative values and adjust after observing soil moisture.
4) Why does the interval get longer when efficiency improves?
Efficiency does not change plant demand; it changes how much water must be applied to deliver the needed net depth. Better efficiency lowers gross depth and runtime, while interval mainly depends on RAW and net daily use.
5) What if the calculator says “no irrigation needed”?
It means net daily use is zero because effective rainfall meets or exceeds ETc. Keep monitoring, because the next dry period may quickly increase demand and require a new interval.
6) Can I use this for newly seeded turf?
Yes, but seedlings may need shorter, lighter cycles than the RAW-based schedule. Use a smaller effective root depth and lower depletion, then confirm with surface moisture checks to prevent crusting and washout.
7) How accurate is the runtime estimate?
Runtime depends heavily on the application rate. Use catch-can measurements for sprinklers or emitter flow data for drip. Recheck after nozzle changes, pressure adjustments, or when wind causes uneven coverage.