Garden Sprinkler run time calculator
Most lawns want about an inch of water a week including rainfall, delivered in one or two deep soakings rather than a daily sprinkle. Shallow, frequent watering trains roots to stay near the surface, which is exactly what you do not want going into a hot spell.
How this is calculated
Total minutes per week = (water needed − rainfall) ÷ precipitation rate × 60. Divide by the number of watering days for each session.
Source: The ~1 inch per week guideline and catch-cup method follow university extension irrigation guidance
Worth knowing: Measure your precipitation rate rather than guessing it — put several straight-sided containers (tuna cans work) around the zone, run it 15 minutes, measure the average depth and multiply by four. Rates vary hugely between head types and even across one zone. On clay or slopes, split the run into two shorter cycles with a gap, or most of it runs off before it soaks in.
Common questions
How do I find my precipitation rate?
Catch-cup test: place several straight-sided containers across the zone, run it for 15 minutes, then measure the water depth in each and average them. Multiply by four for the hourly rate. The spread between cups also tells you how evenly the zone covers — a big spread means a coverage problem no run time will fix.
Is one inch a week right for every lawn?
It is a starting point for cool-season grass in moderate weather. Sandy soil needs more, more often; clay holds water longer but accepts it more slowly. Established warm-season grasses often need appreciably less. Adjust based on whether footprints stay visible on the grass.
Should I water every day?
No. Deep and infrequent beats shallow and daily for almost every established lawn — it drives roots down. New seed is the exception: it needs the surface kept damp, which means light watering several times a day until it germinates.
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