Zerdly

Irrigation Application Volume Calculator

Work out how much water to apply to a paddock at a target irrigation depth, and — if you enter the system flow rate — how long the irrigation must run. Results come in cubic metres, kilolitres and megalitres.

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How to use this calculator

Enter Values

Enter your values and press Calculate to see results.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

  1. Enter the application depth you want to apply, in millimetres.
  2. Enter the irrigated area in hectares.
  3. Optionally enter the system flow rate in litres per second to also get the run time and the flow as ML/day.

How it works

One millimetre of depth over one hectare is 10,000 litres, which is 10 m³, so the volume needed is application depth (mm) × area (ha) × 10, in cubic metres (equal to kilolitres; divide by 1000 for megalitres). With a flow rate in litres per second, the run time is volume in litres ÷ (flow × 3600) hours, and the same flow expressed daily is flow × 86,400 ÷ 1,000,000 = flow × 0.0864 ML/day.

Worked example

Worked example. Applying 30 mm to 8 hectares: volume = 30 × 8 × 10 = 2,400 m³ = 2,400 kL = 2.4 ML. At a 50 L/s flow: run time = 2,400,000 L ÷ (50 × 3600) = 13.33 h, and 50 L/s equals 4.32 ML/day.

Common mistakes

  • Treating the applied depth as what the crop receives — allow ~70–90% irrigation efficiency for uniformity and evaporation/drift losses.
  • Applying more than the soil's readily available water, causing deep drainage and runoff.
  • Mixing up flow units — the run-time formula needs the flow in litres per second.

Frequently asked questions

How is 1 mm over 1 hectare 10,000 litres?

A hectare is 10,000 m², and 1 mm of depth over 1 m² is 1 litre, so 1 mm over 1 ha is 10,000 litres = 10 m³ = 0.01 ML.

Why is the run time longer than my scheduled time?

This is the gross delivered volume ÷ flow. If your system is less than 100% efficient, you need to apply more gross depth to net the target root-zone depth, which lengthens the run.

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Tip: Enter any known values to calculate the remaining results.

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