Calculate irrigation water requirements
Use consistent assumptions for the selected crop and irrigation season. All values are user-entered planning estimates.
1. Farm area and water demand
2. Irrigation schedule and efficiency
Enter the farm area, crop water demand and irrigation assumptions, then calculate.
Volumes are planning estimates. The last irrigation interval may be shorter than the chosen frequency; the seasonal total accounts for the exact number of entered days.
How to Use This Calculator
Enter the area to be irrigated, your estimated crop water demand in millimetres per day and any effective rainfall. Set the number of days between irrigation events, the season length and the estimated irrigation efficiency. Select Calculate to obtain daily, per-event and seasonal irrigation water volumes.
Irrigation Water Requirement Formula
Net irrigation depth (mm/day) = max(0, Crop water demand − Effective rainfall)
Net daily volume (litres) = Net irrigation depth × Area (m²)
Gross daily volume (litres) = Net daily volume ÷ (Efficiency % / 100)
Full-event volume = Gross daily volume × Days between events
Seasonal volume = Gross daily volume × Season length
Volume conversion = 1,000 litres per cubic metre (m³)
Understanding Your Results
Net water demand represents water needed by the crop after effective rainfall. Gross irrigation water is the amount to supply before estimated application losses. Irrigation frequency changes the volume required at each event, but not the total seasonal volume when the same daily water demand is assumed.
Irrigation Planning in Nigeria
Water needs vary across Nigeria with crop type, climate, soil, growth stage and irrigation method. Enter locally appropriate assumptions and confirm water availability, irrigation timing and system design with a qualified agronomist or irrigation professional. This tool does not estimate pump capacity, hydraulic pressure or groundwater sustainability.
Related Finelib Resources
Frequently Asked Questions
What is crop water demand?
The daily depth of water needed by the crop, entered here in millimetres per day. Use a locally appropriate estimate; this calculator does not prescribe one.
What does irrigation efficiency mean?
The percentage of applied irrigation water that effectively reaches the crop root zone. Lower efficiency increases the gross volume required.
How does irrigation frequency affect water use?
Frequency determines the interval and volume per irrigation event. At a constant daily demand, it does not change the calculated average daily requirement.
How do I convert millimetres into litres?
One millimetre of water over one square metre equals one litre.
Does this calculator account for rainfall?
Yes, optionally. Enter an estimated effective rainfall depth per day to subtract from crop water demand, without allowing negative irrigation demand.
Can I use it for drip or sprinkler irrigation?
Yes. Enter an efficiency estimate suitable for the irrigation system, soil and operating conditions.
Does this calculate pump capacity?
No. It calculates water volumes, not pump flow, pressure, power or hydraulic design.