Irrigation Water Calculator

Calculate weekly irrigation water needs based on lawn or garden area, plant water requirements, and rainfall.

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sq ft
inches
inches
%

Weekly Irrigation Water

1,246 gallons

Monthly Irrigation Water5,395 gallons
Season Total (26 weeks)32,396 gallons
Sprinkler Run Time (1.5 GPM)13.8 hours

Weekly Irrigation Water vs Irrigated Area

View formula & how it works →

How to Calculate Irrigation Water Needs

Lawns and gardens need about 1 inch of water per week, including rainfall.

Formula

Weekly Gallons = Area * (Need - Rainfall) * 0.623 / Efficiency

Irrigation Efficiency

  • Drip irrigation: 85-95%
  • Sprinkler: 60-75%
  • Flood/furrow: 40-60%

    • Overwatering is the most common irrigation mistake, wasting both water and money.

    Example Calculation

    3,000 sq ft lawn needing 1 inch/week with 0.5 inches rain at 75% sprinkler efficiency.

    1. 01Water deficit: 1.0 - 0.5 = 0.5 inches
    2. 02Weekly gallons: 3,000 * 0.5 * 0.623 / 0.75 = 1,246 gallons
    3. 03Monthly: 1,246 * 4.33 = 5,395 gallons
    4. 04Season (26 weeks): 1,246 * 26 = 32,396 gallons

    Frequently Asked Questions

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