Irrigation Water Requirement
PROEstimate daily and seasonal crop water demand using the FAO reference ET method.
BAgSci, DipAg, Certified Farm Advisor (NZIPIM)
Agricultural scientist and farm advisor with 18 years across sheep/beef, dairy, and arable operations in New Zealand and Australia.
Unlock Irrigation Water Requirement
Get full results, advanced insights and unlimited access with Numly Pro.
- Access this and 300+ professional calculators
- Advanced insights and detailed breakdowns
- Engineering, trading, clinical and chemistry tools
- Save calculations and track history
- Export results as PDF
- No ads — ever
NZ$9.99/month after trial · Cancel anytime
Related calculators
Fertiliser Rate Calculator
Convert nutrient recommendations to product application rates for common fertilisers.
Spray Dilution & Volume Calculator
Calculate pesticide / herbicide product volume and water required for a spray job.
Livestock Feed Requirement
Calculate daily dry matter (DM) intake and feed budget for cattle, sheep or deer.
About the Irrigation Water Requirement
Crop water requirement (ETc) = Reference ET₀ × Crop coefficient (Kc). ET₀ varies daily with temperature, humidity, wind and solar radiation.
Gross irrigation = Net requirement ÷ Application efficiency. Flood irrigation is ~65% efficient; pivot sprinklers ~80–90%; drip irrigation ~90–95%.
How it works
ET_c = K_c \times ET_0