Irrigation in the Pacific Northwest

System Pumping Requirements

Use this form to calculate the system capacity (flow rate) required to meet the demands of a field. Learn more about the units used on this page.

Another simple way to do this is to estimate the maximum crop water use rate (in/day) you need to keep up with, and convert this to gpm/acre (in/day x 18.9 = gpm/acre). (Precipitation rate conversions here). You then need to divide by the irrigation application efficiency as a decimal (such as 0.75). Many irrigation system designers in Eastern Washington use 6.0 to 7.5 gpm/acre. Go here for a calculator for your crop, soil, and area. This gpm/acre is then just multiplied by the field size to get a system design flow rate in gpm.

Net Irrigation Depth Required Per Week:
Total Area:
Total Hours Available to Operate per Day:
Total Days Available to Operate per Week:
days per week
Irrigation Efficiency:
Total Flow Required to Operate System:



The Equation

This calculator uses this formula to determine the system pumping requirements of a field.


= Total flow rate required to operate irrigation system (gpm)

= The net application required per week (in)

= Total area to be irrigated (acres)

= Total hours available to operate per day (hrs)

= Total days available to operate each week (days)

= Efficiency of the irrigation system (as a deciaml)



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