Drip Irrigation Flow Calculator
Works out flow, emitter count and run time for a drip layout.
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The formula
total flow = emitters × emitter flow rate (mm/h) = emitter flow (L/h) ÷ (emitter spacing × line spacing, in m) run time = depth ÷ (rate × efficiency)
One litre on one square metre is one millimetre. Rate assumes the water is averaged across the bed, though it actually wets strips along the lines.
What to watch out for
Check the total against your supply: if it exceeds it, the system needs zones. Long lines lose pressure, so stay within the maker’s maximum run length. Fit a filter, as emitters block easily.
Frequently Asked Questions
How long should I run drip irrigation?
At 2 L/h emitters, spaced 30 cm on lines 1 m apart, the rate is 6.67 mm/h, so 5 mm at 90% efficiency takes 50 minutes.
How much flow do I need?
Emitters × emitter flow. 1,000 emitters at 2 L/h need 33 L/min.