Run Time for 1" Water: How long to run your sprinklers to deliver one inch of water — the standard weekly deep-watering target for most cool-season grasses.
Number of Heads: Minimum sprinkler heads to cover your lawn area. Actual layouts may need more heads due to irregular shapes or overlapping spray patterns.
Total GPM: Gallons per minute your system demands when all heads run simultaneously. Compare this to your water supply's available flow rate — if GPM exceeds supply, you'll need multiple zones.
Spacing: Recommended distance between heads for head-to-head coverage. Rotary heads throw farther and space wider; pop-ups are closer together.
How This Calculator Works
You enter lawn length and width in feet and choose a sprinkler head type (rotary, fixed, or pop-up). The tool multiplies dimensions for total area, divides by typical coverage per head to get head count, sums the per-head flow rates for total GPM, and uses the formula area ÷ (GPM × 96.3) for run time. The constant 96.3 converts GPM-minutes to square-foot-inches of water.
Quick Questions
Where does the 96.3 constant come from?
One gallon covers about 0.2296 sq ft at 1 inch depth. So 1 GPM running for 1 minute delivers 0.2296 sq ft·in. Multiplied by 60 minutes gives 96.3 sq ft·in per GPM·hour — the conversion factor the run-time formula uses.
What if my lawn isn't rectangular?
Use the closest rectangular approximation, or calculate total square footage separately and divide by the coverage-per-head value for your sprinkler type to estimate head count manually.
How do I know if I have enough water pressure?
Residential water supply typically provides 8–12 GPM at 40–60 PSI. If total GPM exceeds your supply, split the system into zones that run sequentially. Your local water utility can tell you your home's flow rate.
Should I water 1 inch per week all at once?
For most lawns, splitting into 2–3 sessions per week is better for absorption and root development. Watering deeply but less frequently encourages deeper root growth compared to daily light watering.