Irrigation Sizing Calculator
From evapotranspiration to a pump specification: the flow you need, the volume you will move, and what it costs to run.
This performs the arithmetic set out in Water management and turns it into a specification you can quote to a pump supplier.
Irrigation sizing calculator
Sizing for peak crop demand, with optional pumping-energy estimates.
Peak for a full canopy is 6–9 mm/day
Covers filtration losses, flushing and leakage
From the density calculator
Elevation + friction; 0 to skip energy estimate
The formulas#
Daily crop need (m³) = area (m²) × ETc (mm/day) ÷ 1,000
Required flow (m³/h) = daily need ÷ irrigation hours per day
÷ application efficiency
Design flow (m³/h) = required flow × (1 + design margin)
Volume per irrigation = daily need ÷ irrigations per day
L per plant = volume (L) ÷ plant count
Pump power (kW) = 2.725 × flow (m³/h) × head (m) ÷ pump efficiency ÷ 1,000
Daily energy (kWh) = power × hours per day
Cycle energy = daily energy × irrigated daysThe constant 2.725 is ρ·g ÷ 3600 for water at 1000 kg/m³; that product is watts, so divide by 1,000 for kilowatts. Add 10–20% for motor and control losses before choosing a motor.
Worked example#
A 2 ha block at peak 8 mm/day, 12 h/day, micro-sprinkler at 80% efficiency, 20% margin:
Daily need = 20,000 m² × 8 ÷ 1,000 = 160 m³/day
Required = 160 ÷ 12 ÷ 0.80 = 16.7 m³/h
Design flow = 16.7 × 1.20 = 20.0 m³/h (333 L/min)
Pump power = 2.725 × 20 × 25 ÷ 0.65 ÷ 1000 = 2.1 kWThat is the number to give a pump supplier, alongside the head.
Reading the results#
| Output | Why it matters |
|---|---|
| Daily crop need | The volume your source must sustain every day at peak |
| Design flow | The number you give a pump supplier — do not spec on average demand |
| L per plant per irrigation | Sanity-check against the 30–80 L/plant range for banana |
| Emitter capacity | Total L/h your drippers can deliver; must exceed design flow |
| Pump power | Sized on design flow and total dynamic head |
| Cycle volume | Total water and energy for the whole production cycle |
Next steps#
- Understand the demand curve by stage: Water management.
- Install and maintain it: Setting up irrigation.
- Size the block: Planting density calculator.