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Lawn Irrigation Calculator

Calculate weekly water need, gallons per session, and minutes per zone for a lawn sprinkler schedule. Adjusts for soil type, climate zone, and the 0.623 gal per sq ft per inch formula, and warns when one session is longer than the soil can absorb.

Lawn and sprinkler details

A typical US suburban lot lawn is 5,000 to 10,000 sq ft.

Standard turfgrass needs about 1 in per week including rainfall.

Rotor heads run 1 to 5 GPM. Stationary spray heads run 1 to 2 GPM.

Count only heads running in the same zone at the same time.

US average is about $0.005/gal ($5 per 1,000 gallons).

Two deep waterings beat seven shallow ones for root depth.

Sandy soils tolerate 60 min sessions. Clay caps at 25 min.

Arid zones lose more to evaporation. Humid zones get rain support.

Weekly water need

3,115 gal

Run sprinklers for 129.79 min per session (1,557.5 gal per session).

Weekly cost

$15.58

Monthly cost

$67.67

Soil session cap

45 min

Each session (129.79 min) exceeds the 45 min soil soak limit. Split the schedule across 6 days per week so water soaks in instead of running off.

Water early morning (4 to 8 AM) to limit evaporation and fungal growth. Uses the standard 0.623 gallons per sq ft per inch formula, then adjusts for climate zone.

Frequently Asked Questions about the Lawn Irrigation Calculator

How much water does a lawn need per week?
Standard cool-season turfgrass needs about 1 inch of water per week, including rainfall, to stay green and grow a deep root system. Warm-season grasses like Bermuda or Zoysia get by on slightly less, while newly seeded or sodded lawns need more frequent light watering until roots establish. The calculator uses 1 inch as the default and lets you bump it up for stress periods or down if your turf species needs less.
Why does soil type change how long I can run sprinklers?
Sandy soil drains fast, so it can soak up to 60 minutes of watering in one session without runoff. Loam absorbs at a moderate rate, capping around 45 minutes. Clay rejects water once the top layer saturates, so anything over about 25 minutes pools on the surface and runs off down the slope. When the calculator flags an over-runtime warning, split the schedule across more days per week so each session stays under the soak limit.
Where does the 0.623 gallons per square foot per inch number come from?
It is a unit conversion. One cubic foot is 1,728 cubic inches, and one US gallon is 231 cubic inches, so one cubic foot holds 7.4805 gallons. One square foot covered by one inch of water is one-twelfth of a cubic foot, or 7.4805 divided by 12, which equals about 0.6234 gallons (rounded to 0.623). Multiply lawn area in square feet by inches of water by 0.623 and you get gallons needed.
When is the best time of day to water a lawn?
Run sprinklers in the early morning, roughly 4 AM to 8 AM. Wind is usually calm, the sun has not started pulling water off the leaves, and grass blades dry as the day warms, which limits fungal disease. Midday watering loses up to 30 percent to evaporation. Evening watering leaves the lawn wet overnight and invites brown patch, dollar spot, and other turf diseases.
Why are two deep waterings better than seven shallow ones?
Lawn roots grow toward water. If you water lightly every day, roots stay in the top inch of soil because that is where the moisture lives, leaving the lawn fragile during heat waves or any missed day. Two longer sessions a week soak deeper, pulling roots six inches or more into the soil. Deep roots reach moisture that surface roots cannot, so the lawn tolerates drought, heat, and short watering bans much better.

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