Sprinkler runtime calculator
Measure what your sprinkler actually applies, subtract rain already received, and turn the remaining water target into runtime. Repeat the measurement for each zone instead of assuming every head delivers the same amount.
The interactive calculator requires JavaScript. The formula and worked example below are available without it. No sign-up is required.
How to use this calculator
- Set several straight-sided catch cans across one zone and record how long it runs.
- Average the collected water depths in inches; enter that depth and test duration.
- Enter your established-lawn target, measured rain, and sessions. Recheck after changing weather.
The formula
Output in inches per hour = average caught depth ÷ test minutes × 60. Remaining water = max(0, target − rainfall). Minutes per session = remaining water ÷ output × 60 ÷ sessions.
Worked example
A catch-can average of 0.25 inch in 15 minutes is 1 inch per hour. For an illustrative 1-inch weekly target and 0.25 inch of rain, 45 minutes remain. Split over two sessions, that is 22.5 minutes per session.
Measure output in your yard
University of Minnesota Extension describes catch-can testing to audit irrigation. A single can near one sprinkler may not represent the zone. If readings vary widely, investigate coverage instead of lengthening every run.
Rain and soil change the plan
The weekly target is editable because soil, grass, season, and weather differ. Maryland Extension discusses watering established lawns. Check soil moisture and local restrictions; a calculated runtime is not an automatic watering schedule.
Keep water on the lawn
If water pools or runs toward a walkway, pause and allow infiltration. Shorter cycles may help the same planned runtime soak in. Newly seeded lawns and new sod have different needs and are outside this established-lawn tool.
Common questions
What if rain exceeds my weekly target?
The remaining irrigation requirement becomes zero, never a negative number. The calculator then reports zero runtime.
Can I use this for newly seeded grass?
No. New seed and new sod require a different moisture-management plan. Follow the product or installer’s establishment instructions.
Do all sprinkler zones need the same runtime?
No. Measure each zone separately. Head type, coverage, shade, soil, and slope can differ even on the same property.
Sources & method
Calculations use the formulas shown above. These references inform the planning guidance; they do not endorse this tool. References checked on .
- University of Minnesota Extension: auditing home lawn irrigation systems
- University of Maryland Extension: maintaining an established lawn
Keep planning
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