Key Formulas in Sprinkler System Design
Designing a sprinkler system involves several specific calculations to ensure water is delivered efficiently and uniformly. These formulas help you identify the right components for your layout.
Summary of Constants
These numbers are very important in most calculations and to understand the formulas below.
| Constant | Use Case | Meaning |
|---|---|---|
0.433 | Pressure | PSI generated by 1 foot of elevation |
2.31 | Pressure | Feet of head equal to 1 PSI (Inverse of 0.433) |
96.25 | Precip. Rate | Converts GPM/sq ft into Inches/Hour |
231.1 | Drip Precip. Rate | Converts GPH and square inches into Inches/Hour |
0.408 | Velocity | Converts GPM and Diameter into Feet/Second |
0.866 | Spacing | Adjustment factor for triangular sprinkler spacing (sin 60°) |
General Design Formulas
A quick reference for other common formulas used in irrigation design.
Precipitation Rate (Total Area Method)
Calculates the average precipitation rate over a large, potentially irregular area.
Precipitation Rate (Drip Method)
Calculates the precipitation rate for drip irrigation based on emitter flow rate and spacing configuration.
Precipitation Rate (Single Head)
Calculates precipitation rate for a single sprinkler head based on its flow rate and spacing pattern.
Precipitation Rate (Arc Adjustment)
<strong>Adjusts precipitation rate for partial-circle spray patterns.</strong><br/>Quarter heads (90°) have 4× the PR of full-circle heads.<br/>The Arc Adjustment formula is especially important for understanding matched precipitation - it explains why quarter-circle heads need 1/4 the GPM of full-circle heads to maintain uniform PR.
Triangular Row Spacing
Determines the distance between sprinkler rows for triangular patterns to ensure proper overlap.
GPM Needed for Target PR
Calculates the total flow required to achieve a desired precipitation rate over a specific area.
Slope Percentage
Measures the steepness of a slope as a percentage.
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