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Irrigation Calculators

Drip Irrigation Calculator

Calculate drippers, lateral pipe length, system flow and how long to run your drip each day.

Enter your details

Usually the bed or row spacing.

L/h

ET₀ × Kc. Use the irrigation water calculator if unsure.

mm

Well-maintained drip systems are usually 85–95% efficient.

%

Please note: This calculator provides a mathematical estimate based on the values entered. Recommended agricultural application rates can vary by crop, soil, product formulation, location and official agricultural guidance. Check the product label and local agricultural recommendations before application.

For an inline drip system, enter your lateral and dripper spacing, dripper discharge and the crop's daily water need. You'll get the daily run time, the number of drippers, total lateral length and the flow your pump must deliver.

About the Drip Irrigation Calculator

Drip irrigation puts water right at the root zone, so it wastes far less than flood irrigation. But it only works well if it runs for the right length of time. Run it too short and the crop is stressed; run it too long and you waste water, leach fertilizer and waterlog the roots.

The key idea is the application rate – how many millimetres of water the system puts down per hour over the whole area. For an inline system it depends only on dripper discharge and spacing:

Application rate (mm/h) = Dripper discharge (L/h) ÷ (Lateral spacing × Dripper spacing) (m²)

Once you know that, the daily run time is just the crop's water need divided by the application rate (adjusted for efficiency).

The calculator also gives design figures that help when buying or checking a system: total lateral length, number of drippers and the flow the pump and main line must supply. If the system flow is more than your pump can deliver, divide the field into sections (valves) and run them one after another.

Don't know your crop's daily water need? Work it out with the Irrigation Water Requirement Calculator (ET0 × Kc).

How to use the Drip Irrigation Calculator

  1. 1 Enter the area under drip.
  2. 2 Enter the lateral spacing (usually row or bed spacing) and the dripper spacing along the lateral.
  3. 3 Enter the dripper discharge in litres per hour – it's printed on the pipe or in the product sheet.
  4. 4 Enter the crop's daily water need in mm and your system efficiency, then press Calculate.

The formula we use

Drippers = Area ÷ (Lateral spacing × Dripper spacing)
Lateral length = Area ÷ Lateral spacing
System flow (L/h) = Drippers × Dripper discharge
Application rate (mm/h) = Dripper discharge ÷ (Lateral spacing × Dripper spacing)
Run time (h) = (Daily need ÷ Efficiency) ÷ Application rate

Worked example

Vegetables on 1 acre with laterals 1.5 m apart, 2 L/h drippers every 40 cm, crop need 5 mm/day, efficiency 90%.

  1. Drippers = 4,046.86 ÷ (1.5 × 0.4) = 6,745.
  2. Lateral length = 4,046.86 ÷ 1.5 = 2,698 m.
  3. System flow = 6,745 × 2 = 13,490 L/h (13.5 m³/h).
  4. Application rate = 2 ÷ 0.6 = 3.33 mm/h.
  5. Gross daily need = 5 ÷ 0.9 = 5.56 mm, so run time = 5.56 ÷ 3.33 = 1.67 hours (about 1 h 40 min).

If your pump delivers only about 7 m³/h, split the acre into two valve sections and run each for 1 h 40 min.

Things to keep in mind

  • Online drippers in orchards. For trees with a few drippers each, calculate water per plant instead: litres per plant per day ÷ (drippers per plant × discharge) = hours.
  • Pressure matters. Drippers give their rated flow only at the designed pressure. Low pressure at the far end of long laterals means less water there.
  • Clean filters and flush laterals regularly. Clogged drippers quietly reduce the water your crop gets.
  • Split long run times. On light soils, two shorter runs a day keep water in the root zone better than one long run.

Frequently asked questions

How long should I run drip irrigation per day?

Divide the crop's daily water need (in mm, adjusted for efficiency) by your system's application rate. For 5 mm/day and a rate of 3.33 mm/h at 90% efficiency, that's about 1 hour 40 minutes.

How many drippers are needed per acre?

It depends on spacing. With laterals 1.5 m apart and drippers every 40 cm, about 6,745 drippers per acre. At 1.2 m × 30 cm it would be about 11,240.

How much lateral pipe is needed per acre?

Divide 4,047 m² by the lateral spacing. At 1.5 m spacing you need about 2,700 m of lateral per acre, plus a little for connections.

What pump size do I need for drip?

The pump must supply the system flow at the required pressure. If one acre needs 13.5 m³/h and your pump gives 7 m³/h, run the field in two sections.

Last updated . Spotted a mistake or need a unit we don't support? Tell us.