Irrigation Application Rate Calculator
Calculation Results
Application Rate: 0.00 inches per hour
Understanding Irrigation Application Rates
The application rate, or precipitation rate, is a measure of how quickly water is applied to a specific area by your irrigation system. It is usually measured in inches per hour (in/hr). Knowing this number is critical for preventing overwatering, reducing water waste, and ensuring your landscape receives the precise amount of hydration needed for healthy growth.
The Importance of the Application Rate
If your application rate is higher than the soil's infiltration rate, you will experience water runoff, which wastes water and can carry fertilizers or pesticides into local storm drains. Conversely, if your rate is too low, you may not be watering deeply enough to reach the root zone during your allotted watering window.
The Mathematical Formula
The standard formula used in this calculator is:
Rate (in/hr) = (GPM × 96.3) / Area (sq. ft.)
- GPM: The total flow rate of all sprinklers in the zone.
- 96.3: A constant used to convert gallons per minute to inches per hour over a square foot area.
- Area: The total square footage of the zone being watered.
Realistic Calculation Example
Suppose you have a backyard lawn measuring 1,200 square feet. You check your water meter or sprinkler specs and determine the zone outputs 8 Gallons Per Minute (GPM).
Using the formula: (8 × 96.3) / 1,200 = 0.64 inches per hour.
If your grass requires 1 inch of water per week, you would need to run this zone for approximately 93 minutes total per week (1 / 0.64 = 1.56 hours) to meet that requirement.
Tips for Precision Irrigation
- Group Similar Heads: Ensure all sprinkler heads in a single zone have the same precipitation rate (don't mix rotors with fixed sprays).
- Audit Your System: Use "catch cans" (small cups) placed around the yard to verify the actual depth of water hitting the ground, as wind and evaporation can affect the calculated rate.
- Adjust for Slope: On sloped areas, use shorter run times with multiple cycles (Cycle and Soak) to prevent runoff regardless of the application rate.