SHOP FOR ALL IRRIGATION SUPPLIES ON SPRINKLER WAREHOUSE
SHOP NOW

Home > Maintenance > Helpful Worksheets & Irrigation Equations

How To Calculate Slope & Determine Zones Needed

By using the diagrams below, you can accurately measure a slope and calculate how many zones you’ll need to install your irrigation system.ย  Sprinkler Warehouse recommends that you download these helpful worksheets & the irrigation equations to follow these charts step by step.
Determine the Percentage of Slope
Divide the measure of height by the measure of the length and multiply by 100.

Example Above: 2 Divided By 14 Times 100 = 14.3%

Blank
Graph Paper
Download PDF
Irrigation
Checklist
Download PDF
Timer to Valve Wire Sizing Chart
Gauge Maximum Distance
18 1000 ft
14 1450 ft
10 1750 ft
10 1750 ft
Valve Inlet Size
Size of Inlet Gallons Per Minute (GPM)
3/4″ > 0-10
1″ > 10-20
1 1/2″ > 20-30
2″ > 30-150
PVC Pipe / Schedule 40 PVC Pipe / Class 200
Max GPM Flow Pipe Size Valve Size Max GPM Flow Pipe Size Valve Size
> 0-4 1/2″ 1/2″ > 0-6 1/2″ 3/4″
> 4-8 3/4″ 3/4″ > 6-10 3/4″ 3/4″
> 8-12 1″ 1″ > 10-16 1″ 1″
> 12-22 1 1/4″ 1″ > 16-26 1 1/4″ 1″
> 22-30 1 1/2″ 1 1/2″ > 26-35 1 1/2″ 1 1/2″
> 30-50 2″ 2″ > 35-55 2″ 2″

Use this chart to size your pipe according to GPM needed for each zone.

PVC Pipe / Class 125 Poly Pipe / Galvanized Pipe
Max GPM Flow Pipe Size Valve Size Max GPM Flow Pipe Size Valve Size
> 0-4 1/2″ 1/2″
>0-10 3/4″ 3/4″ > 4-8 3/4″ 3/4″
>10-15 1″ 1″ > 8-12 1″ 1″
>15-24 1 1/4″ 1″ >12-22 1 1/4″ 1 1/4″
> 22-30 1 1/2″ 1 1/2″
> 35-50 2″ 2″

Use this chart to size your pipe according to GPM needed for each zone.

Flow Rates for Service Lines
Length of String 2 3/4″ 2 1/4″ 3 1/2″ 4″ 4 3/8″ 5″
Size of Copper 3/4″ 1″ 1 1/4″
Size of Galvanized 3/4″ 1″ 1 1/4″
Size of PVC 3/4″ 1″ 1 1/4″

Determining The Amount Of Zones

Product Performance Charts

Use this article in addition to the Basic Steps Irrigation Installation Checklist.

Pictured above are helpful worksheets & irrigation equations.