Rainfall & Irrigation Calculator

Calculate lawn irrigation needs based on rainfall, lawn size, and target watering. See weekly water deficit, watering time, and cost.

Inputs

Lawn Area

sq ft

Weekly Rainfall

inches

Target Watering

in/week

Sprinkler Rate

in/hour

Tab to move between fields

Results

Water Deficit

0.5 in/week

Watering Time20 minutes

Gallons Needed/Week1,558

Est. Monthly Cost$31.15

How to Use This Calculator

Enter your Lawn Area in square feet.
Set the Weekly Rainfall your area has been receiving in inches.
Enter the Target Watering amount in inches per week (most lawns need 1–1.5 inches).
Set your Sprinkler Rate in inches per hour.
Review the Water Deficit, required Watering Time in minutes, Gallons Needed per week, and Estimated Monthly Cost.

How the result changes with Target Watering

Target Watering	Water Deficit
0.75	0.25 in/week
1.38	0.88 in/week
2.13	1.63 in/week
2.75	2.25 in/week

What each input means

Lawn Area: Total lawn area.
Weekly Rainfall: Average weekly rainfall.
Target Watering: Most lawns need 1-1.5 inches per week.
Sprinkler Rate: Sprinkler water output rate.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Lawn Area = 5000, Weekly Rainfall = 0.5, Target Watering = 1, Sprinkler Rate = 1.5 = 4 input(s) provided
Calculate Water Deficit
Water Deficit
0.5 = 0.5
Calculate Watering Time
20 = 20
Calculate Gallons Needed/Week
Gallons Needed/Week
1558 = 1558

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