Irrigation Water Calculator
Calculates weekly sprinkler irrigation water volume (standard 1.0" to 1.5" weekly water requirement for healthy turfgrass), watering cycle minutes per zone based on sprinkler head precipitation rate (in/hr), and monthly municipal water utility costs.
Formula
Gallons = Area × (Inches ÷ 12) × 7.48 × (1 + Loss %); Weekly Minutes = (Inches ÷ Precip Rate) × 60
1. 1 Inch of Water over 1 Sq Ft = 0.623 Gallons 2. Net Weekly Gallons = Lawn Area Sq Ft × Weekly Inches × 0.623 3. Total Gallons with Evaporation Loss = Net Gallons × (1 + Loss %) 4. Total Weekly Run Time (Minutes) = (Weekly Inches ÷ Precip Rate in/hr) × 60 5. Minutes per Cycle = Total Weekly Run Time ÷ Watering Days per Week
Inputs
- Lawn / Irrigated Area
- Weekly Water Target Depth
- Sprinkler Head Precipitation Rate
- Watering Days per Week
Worked example
Calculating water volume and sprinkler timer run-time for a 5,000 sq ft lawn.
Outcome: Net water is 3,115 gallons/week (3,582 gallons with 15% evaporation loss). Weekly runtime needed is 100 minutes total. Scheduled across 3 days = ~33 minutes per zone per watering day.
What is the "tuna can test" for lawn sprinklers?
Place 4 to 5 empty tuna or cat food cans around your lawn zone and run the sprinklers for 15 minutes. Measure the water depth in the cans with a ruler and multiply by 4 to discover your exact sprinkler precipitation rate per hour.