Designing a Sprinkler System: Determining Heads and Zones for a 3/4-Acre Lawn

Calculating Sprinkler Heads and Zones Based on Water Supply

Proper irrigation design requires knowing your water supply’s flow rate (GPM) and pressure (PSI). Without this data, any head/zone estimate is guesswork.

Measure Your Flow Rate

1. Get a 5‑gallon bucket.
2. Open an outdoor faucet fully and time how long it takes to fill the bucket.
3. Calculate GPM: GPM = (5 gallons / seconds to fill) × 60.

Determine Pressure

Attach a pressure gauge to the same faucet (or ask your water provider for the static pressure).

Pipe Size Matters

Note the diameter of the service line from the meter to the house (typically ¾″ or 1″). This limits maximum flow.

Next Steps

With GPM, PSI, and pipe size, you can select nozzles from performance charts (e.g., Rain Bird 1800 series) and calculate how many heads per zone stay within your flow limit. Each zone’s total GPM must not exceed the available flow.