Irrigation Pivot Sizing Calculator

Pivot length from field radius and water source.

Field length (ft)

Peak ET (in/day)

System run time (hrs/day)

Application efficiency (%)

Outer tower speed (ft/min)

Number of spans

Tab to move between fields

Irrigated area (acres)

125.7

Required flow (GPM)1,004

Rotation time (hours)23

Span length (ft)189

Total coverage w/ end gun131.9

% of quarter section82.5

App Per Rev0.41

How to Use This Calculator

Enter Field Length (ft) — the shorter dimension; pivot radius is half this (a quarter section = 2,640 ft).
Set Peak ET (in/day) for your crop at peak demand (corn peak: 0.25–0.35 in/day).
Enter System Run Time (hrs/day), Application Efficiency (%), and Number of Spans.
Set Outer Tower Speed (ft/min) — slower speeds apply more water per pass.
Review Irrigated Acres, Required Flow (GPM), Rotation Time (hours), and Coverage % of Quarter Section.

How the result changes with Field length (ft)

Field length (ft): Shorter dimension of the field in feet. Pivot radius is half this. A quarter section is 2,640 ft.
Peak ET (in/day): Peak evapotranspiration rate in inches per day. Corn peak: 0.25-0.35 in/day.
System run time (hrs/day): Hours per day the pivot system operates.
Application efficiency (%): Water application efficiency. LEPA: 90-98%, spray: 80-88%, impact: 75-85%.
Outer tower speed (ft/min): Speed of the outermost tower in feet per minute.
Number of spans: Number of pivot spans (towers). Standard pivots have 5-9 spans.

Irrigated area (acres): Circular area covered by the pivot in acres.
Required flow (GPM): System flow rate in gallons per minute to meet peak crop water demand.
Rotation time (hours): Time for one complete 360° revolution at the set speed.
Span length (ft): Length of each individual pivot span.
Total coverage w/ end gun: Total irrigated acres including estimated end-gun bonus area.
% of quarter section: Percentage of a standard 160-acre quarter section covered.

Identify Input Parameters
4 parameters
Field length (ft) = 2640, Peak ET (in/day) = 0.3, System run time (hrs/day) = 20, Application efficiency (%) = 85 = 6 input(s) provided
Calculate Irrigated area
Irrigated area = areaFt2 / 43560
125.7 = 125.7
Calculate Required flow
Required flow = (areaAcres * grossAppInDay * 452.6) / systemRunHrs
1004 = 1004
Calculate Rotation time
Rotation time = outerCircumference / (pivotSpeedFtMin * 60)
23 = 23