Irrigation Zone Coverage Calculator
Calculate the total irrigated area, water application rate, and flow requirements for a sprinkler zone based on head type, spacing, and layout.
Formulas Used
Area per Head (sector):
Ahead = (arc° / 360°) × π × r²
Effective Zone Coverage:
Azone = N × Ahead × (1 − overlap%/100)
Accounts for overlapping coverage counted only once.
Precipitation Rate (in/hr):
PR = (96.25 × Qzone) / Azone
where Qzone = N × GPMhead (total zone flow in GPM)
Constant 96.25 derived from unit conversion: (231 in³/gal × 60 min/hr) / 144 in²/ft²
Water Applied per Cycle (inches):
Applied = PR × (run time / 60)
Distribution Uniformity (DU) — simplified model:
DU = min(0.55 + 0.60 × overlap%/100, 0.92)
Based on industry correlation between overlap and uniformity (ASABE/IA standards).
Recommended Head Spacing:
Spacing = 2r × (1 − overlap%/100)
Assumptions & References
- Sprinkler heads are assumed to have uniform, circular throw patterns at the specified radius and arc.
- The effective area formula uses a linear overlap deduction model — actual field coverage depends on head layout geometry (square, triangular, etc.).
- The precipitation rate constant 96.25 is derived from: (231 in³/gal × 60 min/hr) ÷ 144 in²/ft² = 96.25.
- Distribution Uniformity (DU) estimate is a simplified model; field measurement via catch-can test is recommended per ASABE S436.1 and Irrigation Association (IA) guidelines.
- Head-to-head spacing at 50% overlap is the industry best practice per the Irrigation Association and Hunter/Rain Bird design guides.
- Typical residential water supply: 15–20 GPM at 40–60 PSI (varies by meter size and service line).
- Soil infiltration rates: sand ~2 in/hr, loam ~0.5 in/hr, clay ~0.2 in/hr (USDA NRCS).
- Reference: Irrigation Association (IA) — Landscape Irrigation Best Management Practices; ASABE Standard S436.1.