Lawn Watering Calculator
Water needed for your lawn
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Lawn Watering Calculator is built for water needed for your lawn — fast, free, and private. You supply Lawn Length (ft), Lawn Width (ft) and Water (in/week) to Lawn Watering; the answer follows at once. Every Lawn Watering answer can be reproduced by hand. Lawn Watering shines when speed matters. Nothing is uploaded while Lawn Watering works, and the figures stay put. Looking for lawn watering calculator gallons sprinkler inches or a quick estimate? Lawn Watering covers both. Keep Lawn Watering bookmarked for next time. Lawn Watering is free, instant and local.
What the defaults give
A 40 × 30 ft lawn — 1,200 sq ft — needs 748 gallons a week for 1 inch of water, which is about 150 minutes at 5 gallons a minute.
One inch over one square foot is 0.623 gallons, and that constant does all the work.
The formula
Area = length × width
Gallons = area × inches × 0.623
The 0.623 comes from the volume of water one inch deep over a square foot: 144 cubic inches divided by 231 cubic inches per gallon. Everything else is multiplication, so the answer scales exactly with area and with the depth you ask for.
Worked examples
1,200 sq ft at 1 in → 748 gal
600 sq ft at 1 in → 374 gal
2,400 sq ft at 1 in → 1,495 gal
1,200 sq ft at 0.5 in → 374 gal
1,200 sq ft at 2 in → 1,495 gal
Doubling the area and doubling the depth produce the same total, which is the useful property when you are deciding whether to water more ground less deeply or less ground more deeply. For establishment, deeper and less frequent is the better trade: it pushes roots down.
Turning gallons into minutes
The tool divides by 5 gallons a minute, a typical hose-end or small sprinkler output. Measure yours: put a container of known size under the sprinkler, time how long it takes to fill, and the rate follows. A system delivering 8 gpm needs 94 minutes for the same 748 gallons; one delivering 3 gpm needs 249.
Watering in one weekly pass beats several short ones, because evaporation losses are lower and the water reaches depth. Early morning is the best window — evening watering leaves blades wet overnight, which favours fungal disease.
What the number leaves out
This is a gross requirement, not a net one. Rainfall counts toward it: an inch of rain delivers exactly what an inch of irrigation does, so subtract it. Slope, wind, soil type and mulch all change how much of the applied water the roots actually get — sandy soil drains past the root zone, clay runs off.
Most established cool-season lawns survive on 1–1.5 inches a week including rain, and many survive on less by going dormant in summer. Watering to keep a lawn green through a drought can use more water than the rest of the house combined.
Frequently Asked Questions
How many gallons does a 1,200 sq ft lawn need?
About 748 gallons a week for one inch of water, which is roughly 150 minutes at 5 gallons a minute.
How long should I run the sprinkler?
Divide the gallons by your measured flow rate. At 5 gpm that is 150 minutes; at 3 gpm it is 249 minutes for the same depth.
Does rain count?
Yes. An inch of rain delivers an inch of water, so subtract the week’s rainfall from the irrigation you apply.
Is one deep watering better than several light ones?
Yes, for established lawns. Deeper, less frequent watering pushes roots down and loses less to evaporation.
How much water does a lawn really need?
Most cool-season lawns need 1–1.5 inches a week including rain. Some go dormant in summer and recover when the weather cools.
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