Irrigation Calculator
Calculate how many sprinkler heads you need, total GPM flow rate, weekly water usage, and irrigation costs. Covers rotary heads, fixed spray, and drip irrigation systems.
sq ft
PSI
Sprinkler Heads Needed
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Total Flow Rate —
Weekly Water Usage —
Extended More scenarios, charts & detailed breakdown ▾
sq ft
PSI
$
Sprinkler Heads Needed
—
Zones Needed —
Weekly Water Usage —
Monthly Water Cost —
Professional Full parameters & maximum detail ▾
sq ft
in/hr
in
ft
$
Run Time per Zone
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Weekly Gallons —
Annual Water Cost —
Smart Controller Annual Savings —
Recommended Pipe Size —
How to Use This Calculator
- Enter your lawn area in square feet.
- Select sprinkler type (rotary heads cover more area; fixed spray use more water per zone).
- Enter your water pressure in PSI (check your hose bib with a gauge).
- See sprinkler heads needed, total GPM, and estimated weekly water usage.
- Use Drip Irrigation tab to plan garden bed emitter systems.
- Use Water Budget tab to estimate monthly and seasonal irrigation costs.
Formula
Heads Needed = Lawn Area ÷ Coverage per Head
Run Time = Weekly Water Need (in) ÷ Precipitation Rate (in/hr) × 60 min
Weekly Gallons = Total GPM × Run Time (min)
Example
5,000 sq ft lawn with rotary heads (400 sq ft coverage, 1.5 GPM each): 5000÷400 = 13 heads, 13×1.5 = 19.5 GPM. At 1 in/week need and 0.6 in/hr precip rate: run time = 100 min/week. Weekly gallons = 19.5×100 = 1,950 gallons.
Frequently Asked Questions
- Divide your lawn area by the coverage per head. Rotary heads cover ~400 sq ft each; fixed spray heads cover ~100 sq ft each. A 5,000 sq ft lawn needs about 13 rotor heads or 50 fixed spray heads. Always add 10–15% overlap for even coverage.
- GPM (gallons per minute) is the flow rate your system demands. Your water meter and supply line have a maximum GPM capacity (typically 10–15 GPM for residential). If your system exceeds this, you need multiple zones.
- Most lawns need 1–1.5 inches of water per week. Divide by your system's precipitation rate (inches/hour) to get run time. A rotor with 0.5 in/hr precipitation rate needs 2 hours per week per zone.
- Precipitation rate is how many inches of water your sprinklers apply per hour (typically 0.4–2.0 in/hr). Lower rates give water more time to soak in and reduce runoff. Match precipitation rates across zones for uniform watering.
- Yes — EPA WaterSense certified smart controllers reduce outdoor water use by 15–30% by adjusting schedules based on real-time weather, soil moisture, and evapotranspiration rates. They pay for themselves in 1–3 seasons.