How this calculator works
One inch of water over one square foot is 144 cubic inches, which is about 0.623 gallons. The calculator multiplies by your area and weekly inches, then divides by your flow rate to get watering time.
Gallons per week = Area × Inches × 0.623
Minutes = Gallons ÷ Flow rate ÷ Watering days
Worked example
Using the default values in the calculator above:
| Input | Value |
|---|---|
| Area to water | 200 sq ft |
| Water per week | 1 in |
| Flow rate | 5 gal/min |
| Watering days per week | 2 |
| Result | Value |
|---|---|
| Water per week | 125 gallons |
| Minutes per watering | 12.5 min |
| Gallons per watering | 62 gallons |
Step by step:
- Gallons per week = 200 × 1 × 0.623 = 124.6
- Per watering = 124.6 ÷ 2 = 62.3 gal
- Minutes = 62.3 ÷ 5 gpm = 12.46
Gallons for 1 inch of water
| Area | Water per week |
|---|---|
| 100 sq ft | 62 gallons |
| 500 sq ft | 312 gallons |
| 1,000 sq ft | 623 gallons |
| 2,500 sq ft | 1,558 gallons |
| 5,000 sq ft | 3,115 gallons |
Common mistakes to avoid
- Watering a little every day, which keeps roots shallow.
- Not subtracting rainfall.
Frequently asked questions
How many gallons is an inch of water on 1,000 sq ft?
About 623 gallons.
How do I measure my sprinkler’s output?
Set straight-sided cans around the area, run the sprinkler 15 minutes and measure the depth collected.