Irrigation Calculator

How Irrigation Watering Time Is Calculated

This calculator estimates how long to run your sprinkler or irrigation system, and how much water you'll use, based on your garden or lawn's area, a target water depth, and your system's flow rate. A common gardening guideline is about 1 inch of water per week for most lawns and gardens, though this varies by plant type, soil, climate, and season — treat it as an adjustable starting point rather than a fixed rule. One inch of water over a square foot of area equals roughly 0.623 gallons, which is how total water volume is derived from area and water depth.

Example

A 1,000 sq ft lawn needing 1 inch of water per week requires 1,000 × 1 × 0.623 ≈ 623 gallons for the week. With a sprinkler system delivering 10 gallons per minute, that takes about 62.3 minutes of total watering time — which you might split across two or three sessions during the week.

Common Use Cases

FAQs

Is 1 inch of water per week always correct?

It's a commonly cited average for many lawns and gardens, but actual needs vary by grass or plant type, soil drainage, rainfall, temperature, and season — hot, dry periods often need more, while cooler or rainy periods need less. Adjust the water depth input to match your specific situation.

Should I water in one long session or split it up?

This calculator gives the total time needed for the full weekly amount — many gardeners split that total across two or three shorter sessions per week rather than one long watering, which can help water soak in more effectively and reduce runoff, especially on compacted or sloped soil.

How do I find my sprinkler's flow rate?

Check the manufacturer's spec sheet, or measure it yourself by timing how long it takes to fill a container of known volume (like a 5-gallon bucket) from the sprinkler head, then converting to a per-minute rate.