Irrigation Run Time Calculator
Calculate how long to run your irrigation system to apply a desired amount of water to your lawn or garden.
Fill in the fields above and click Calculate.
Formula
Effective Precipitation Rate (in/hr) = Precipitation Rate × (Efficiency / 100)
Run Time (hours) = Desired Water Application (in) ÷ Effective Precipitation Rate (in/hr)
Run Time (minutes) = Run Time (hours) × 60
Example: To apply 1.0 inch with a sprinkler rated at 1.5 in/hr and 75% efficiency:
Effective Rate = 1.5 × 0.75 = 1.125 in/hr
Run Time = 1.0 ÷ 1.125 = 0.889 hr ≈ 53.3 minutes
Assumptions & References
- The precipitation rate (also called application rate) is provided by the sprinkler manufacturer or measured via catch-cup test.
- System efficiency accounts for losses due to wind drift, evaporation, and uneven distribution. Typical values: rotary heads 75–85%, fixed spray heads 65–75%, drip systems 90–95%.
- A common lawn irrigation target is 1 inch per week, applied in 1–3 sessions to encourage deep root growth.
- Precipitation rates vary widely: fixed spray heads ~1.5–2.5 in/hr; rotary/rotor heads ~0.4–1.0 in/hr; drip systems ~0.1–0.5 in/hr.
- Formula reference: Irrigation Association, Landscape Irrigation Scheduling and Water Management (2014).
- This calculator assumes uniform distribution across the irrigated area. Conduct a catch-cup audit for precise measurements.