How to use this calculator
- Enter the area and the lateral and dripper spacing you plan to use.
- Choose the dripper flow rate.
- Split the field into zones if the pump is small.
- Enter the daily water depth to get run time.
How do you calculate drip irrigation flow and run time?
Drippers = Area ÷ (Srow × Sdripper)
Application rate (mm/h) = q ÷ (Srow × Sdripper)
Run time (h) = depth needed (mm) ÷ application rate
q is dripper flow in L/h, spacings in metres. A litre spread over one square metre is one millimetre.
Worked example
With area under drip 1 acre, lateral (row) spacing 1.5 m, dripper spacing along the lateral 0.5 m, dripper flow 4 L/h, number of zones (valves) 1, water to apply per day 5 mm:
Pump flow per zone: 21.58 m³/h
The calculator also gives number of drippers 5,396 nos; total lateral length 2,698 m; flow per zone 6 L/s.
Assumptions and limits
- Assumes one dripper per spacing point on every lateral, covering the whole area.
- Pressure compensating drippers are assumed, so all drippers give their rated flow.
- Add 10 to 15% to pump flow for filter flushing and pipe losses.
Frequently asked questions
How many drippers are needed per acre?
It depends on spacing. At 1.5 m between laterals and 0.5 m between drippers, an acre (4,047 m²) needs about 5,400 drippers. At 1.2 m × 0.4 m it needs about 8,400.
How long should I run drip irrigation?
Divide the daily water need in mm by the application rate in mm/h. For 5 mm a day at an application rate of 5.3 mm/h, run each zone for about 56 minutes.
What pressure does drip irrigation need?
Most inline drippers work at 1 to 1.5 bar (10 to 15 m head). Pressure compensating drippers usually work from 0.5 to 4 bar.
References
- FAO Irrigation and Drainage Paper 56
- Indian National Committee on Irrigation and Drainage, drip irrigation guidelines