Find the highest watering need for your site. Compare demands, adjust efficiency, and include rainfall. Size pumps and timers with confidence on peak days.
| Area (m²) | ET0 (mm/day) | Kc | Rain (mm/day) | Eff. (%) | Peak (%) | Hours/day | Peak demand (L/day) | Flow (L/min) |
|---|---|---|---|---|---|---|---|---|
| 150 | 6.0 | 0.80 | 0.50 | 75 | 15 | 2.5 | 989 | 6.6 |
1) Peak multiplier:
PeakMultiplier = 1 + (PeakFactor% / 100)
2) Net irrigation depth (mm/day):
NetDepth = max(0, (ET0 × Kc − EffectiveRain) × PeakMultiplier)
3) Gross depth (mm/day):
GrossDepth = NetDepth ÷ (Efficiency% / 100)
4) Peak day volume:
LitersPerDay = GrossDepth × Area
Because 1 mm over 1 m² equals 1 liter.
5) Required flow for the watering window:
Flow(L/s) = LitersPerDay ÷ (Hours × 3600)
Peak day demand is the maximum daily water requirement your landscape can experience during the hottest, driest conditions. Planning for this peak helps you size pumps, mainlines, valves, and storage so the system maintains pressure while meeting plant needs. When peak demand is underestimated, zones may run longer, distribution uniformity drops, and sensitive plants show stress even if average use looks acceptable. It also helps compare seasonal changes and document upgrades over time clearly.
The peak is influenced by reference evapotranspiration, plant type, microclimate, wind exposure, and soil water-holding capacity. Turf and shallow-rooted ornamentals typically peak higher than established shrubs or native beds. Slopes and sandy soils often increase peak frequency because they store less water, requiring shorter, more frequent cycles to avoid runoff and deep percolation losses.
A practical approach is to convert a target gross irrigation depth into a daily volume using the irrigated area. In this calculator, gross depth reflects the net plant water need adjusted for irrigation efficiency, so the estimated peak volume includes common losses. This makes the result useful for planning supply capacity, storage drawdown, and day-to-day scheduling constraints.
Once peak daily volume is known, convert it into a required flow by dividing by allowable irrigation hours per day. If you restrict runtime to off-peak utility windows, the required flow rises, which may shift you toward larger pipe diameters, higher pump duty points, or additional zones. Peak demand also supports reservoir sizing by comparing daily drawdown to refill rates.
Peak demand can be managed without sacrificing plant health by improving distribution uniformity, repairing leaks, upgrading nozzles, and using cycle-and-soak scheduling on slopes. Mulching and soil organic matter improvements reduce evaporative losses and increase storage, lowering peak frequency. Smart controllers that track weather can trim unnecessary runtime and keep the system closer to true peak requirements.
It is the maximum daily water volume your landscape may need under extreme heat and low humidity. It supports sizing of pumps, pipes, storage, and irrigation schedules so every zone receives adequate water at design pressure.
Use measured system performance when possible. Typical values range from 0.60–0.85 depending on emitter type and maintenance. Lower efficiency increases gross depth and peak volume, reflecting losses from wind drift, evaporation, runoff, and non-uniform coverage.
Peak volume must be delivered within the hours you can run the system. Fewer hours means the same daily volume needs a higher flow rate, which can require larger pipes, more zones, or a higher-capacity pump.
Use net depth for plant water need, then convert to gross depth by dividing by efficiency. This calculator accepts gross depth directly, so the output already accounts for common application losses and is better for supply planning.
Review at the start of each hot season, after major planting changes, and after equipment upgrades. Adjust for new microclimates, soil amendments, or nozzle changes that alter distribution uniformity and effective irrigation efficiency.
Improve uniformity, fix leaks, add mulch, increase soil organic matter, and use cycle-and-soak on slopes. Weather-based control can shorten unnecessary runtime while maintaining adequate moisture during true peak conditions.
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.