💧 Lawn Watering Schedule Calculator
Most lawns need about 1–1.5 inches of water per week. Enter your lawn area, target amount, and recent rainfall to see how many gallons of supplemental watering you need.
Rain first, then the difference in gallons
Rainfall is subtracted from the weekly target, and only the shortfall is converted to gallons:
shortfall in = max(0, target in - rainfall in)
gallons = area sq ft × shortfall in × 0.623With the defaults - 1,000 sq ft, a 1.5 in target and 0.5 in of rain - the shortfall is 1.00 in and you owe the lawn 623 gallons. That is the number worth remembering: 623 gallons per inch per 1,000 sq ft. If rain exceeded the target the shortfall is held at zero rather than going negative.
| Lawn area | Gallons per inch |
|---|---|
| 1,000 sq ft | 623 |
| 5,000 sq ft | 3,115 |
| 10,000 sq ft | 6,230 |
Turning gallons into sprinkler minutes
- Measure your output. Set several straight sided cans around the zone, run it 15 minutes, and average the depths. A quarter inch in 15 minutes is 1 in per hour, so an inch takes an hour.
- Split it. Two sessions a week beat seven light ones - deep water pulls roots down, daily sprinkles keep them at the surface.
- Water early. Before mid morning loses least to evaporation and lets the blades dry, which matters for disease.
Frequently asked questions
How many gallons is one inch of water on 5,000 sq ft?
3,115 gallons. An inch of water is 0.623 gallons over each square foot, whatever the shape of the lawn.
How long should I run the sprinklers?
Long enough to deliver the shortfall, which only a catch can test tells you. A zone measured at 0.5 in per hour needs two hours for an inch, best given as two runs on separate days.
Does my lawn really need 1.5 inches a week?
That is the upper end. Cool season grass in mild weather does well on about an inch, established lawns tolerate less and go dormant rather than die, and new seed needs frequent light watering instead. Local restrictions on watering days come first.