Calculator Inputs
Large screens show three columns, smaller screens show two, and mobile shows one.
Example Data Table
| Flow (LPM) | Runtime (min) | System | Outlets | Area | US GPM | Selected gallons per run |
|---|---|---|---|---|---|---|
| 12 | 30 | US | 4 | 120 ft² | 3.1701 | 95.1020 |
| 20 | 25 | Imperial | 5 | 20 m² | 5.2834 | 109.9846 |
| 35 | 15 | US | 7 | 250 ft² | 9.2460 | 138.6903 |
| 8 | 45 | US | 2 | 10 m² | 2.1134 | 95.1019 |
Formula Used
US gallons per minute = LPM × 0.2641720524
Imperial gallons per minute = LPM × 0.2199692483
Liters per hour = LPM × 60
Total gallons per run = selected GPM × runtime minutes
Gallons per outlet per minute = selected GPM ÷ outlet count
Application depth in millimeters = liters per run ÷ area in m²
One liter spread over one square meter equals one millimeter of water depth. That makes area-based irrigation planning simple and useful for beds, lawns, and drip zones.
How to Use This Calculator
- Enter the zone flow rate in liters per minute.
- Enter how long that zone runs each watering cycle.
- Select how many days each week you water.
- Enter outlet count to estimate per-outlet flow.
- Choose US or Imperial gallons for your output totals.
- Optionally add irrigated area to calculate water depth.
- Pick your decimal precision and submit the form.
- Review the result cards, graph, and download the report if needed.
Frequently Asked Questions
1. How is LPM to GPM calculated?
Multiply liters per minute by 0.2641720524 for US gallons per minute. Multiply by 0.2199692483 for Imperial gallons per minute. The calculator shows both values so you can compare standards immediately.
2. Which gallon system should gardeners use?
Most irrigation products in the United States use US gallons. Some older references and UK materials use Imperial gallons. Use the system that matches your pump chart, timer manual, or watering plan.
3. Why does outlet count matter?
Outlet count helps estimate how much flow each sprinkler, dripper, or emitter receives. If the total zone flow stays fixed, more outlets usually mean less water available per outlet.
4. What does application depth mean?
Application depth tells you how much water reaches the soil surface across the irrigated area. It is useful for comparing watering schedules with plant needs and avoiding overwatering or runoff.
5. Can I use this for drip irrigation?
Yes. It works well for drip lines, emitters, hose-fed zones, and small garden manifolds. Enter the total zone flow and use outlet count to estimate the share delivered by each outlet.
6. Does runtime change the conversion?
Runtime does not change the conversion rate itself. It changes the total water delivered during each cycle. Longer runtime increases liters per run, gallons per run, and weekly or monthly totals.
7. Why are US and Imperial results different?
A US gallon and an Imperial gallon are not the same size. An Imperial gallon is larger, so the same liters per minute produce fewer Imperial gallons per minute.
8. Can this calculator help size watering schedules?
Yes. The weekly and monthly total outputs help you compare water use across schedules. Combined with area-based depth, they can support better cycle lengths for beds, containers, and lawns.