Calculator
3 columns on large • 2 on medium • 1 on mobileUse this to estimate irrigation flow, compare hardware options, and document seasonal changes.
Example data table
Sample scenarios show how different inputs map to GPH.
| Scenario | Inputs | Loss (%) | Gross (GPH) | Adjusted (GPH) |
|---|---|---|---|---|
| Hose conversion | 6.5 GPM | 8 | 390.0000 | 358.8000 |
| Bucket test | 10 gallons in 90 seconds | 0 | 400.0000 | 400.0000 |
| Drip zone | 40 emitters × 2.0 GPH | 10 | 80.0000 | 72.0000 |
Formula used
GPH = value × factor
- GPM → GPH: factor = 60
- LPH → GPH: factor = 1 ÷ 3.785411784
- LPM → GPH: factor = 60 ÷ 3.785411784
GPH = gallons ÷ hours
- Liters → gallons: gallons = liters × 0.2641720524
- Seconds → hours: hours = seconds ÷ 3600
Gross GPH = emitters × per-emitter GPH
Adjusted GPH = Gross GPH × (1 − loss%/100)
How to use this calculator
- Select the method that matches your measurement.
- Enter values carefully, using consistent units.
- Optionally add a loss factor for realistic planning.
- Press Calculate to view results above the form.
- Use CSV or PDF exports to save your irrigation notes.
Flow rate planning for garden zones
Gallons per hour (GPH) helps you translate a water source into run times and zone sizes. If a bed needs 120 gallons per watering and your adjusted flow is 360 GPH, the target runtime is 20 minutes. Use this calculator to compare hose bibs, pumps, and drip manifolds before committing to hardware. When planning multiple zones, total demand should stay below the available adjusted flow to avoid uneven coverage and nuisance pressure drops.
Measuring real-world output
Manufacturer labels are a starting point, but field checks improve accuracy. A bucket test measures volume over time and reveals restrictions like partially opened valves or clogged filters. Repeat the test at the same spigot setting and note temperature and hose length for consistent comparisons. For pumps, measure at the working height and with the same fittings you will actually use.
Loss factors and pressure impacts
Flow rarely matches the “best case” value, especially across long hoses, elevation changes, and pressure regulators. The loss factor input lets you reduce gross flow to a planning value that better matches reality. Typical adjustments range from 5–15% for minor friction to 20% or more for complex layouts and aging lines. If your system includes drip tape or micro-sprays, confirm the regulator pressure and apply a conservative loss so each emitter operates near its rated output.
Interpreting conversions for equipment sizing
GPH is useful for irrigation scheduling, while gallons per minute (GPM) often appears on faucets and pump curves. Liters per hour is common on drip emitters, and cubic meters per hour can show up on larger systems. Seeing all conversions together helps you align timers, filters, and pumps to the same reference flow.
Recordkeeping and seasonal optimization
Save CSV or PDF outputs to track changes over a season. If spring flow is higher than midsummer flow, your notes can point to municipal pressure shifts, filter loading, or worn fittings. Over time, a small library of results makes troubleshooting faster and supports smarter upgrades when expanding zones. Recording the loss factor you used also helps you keep future comparisons consistent across maintenance cycles.
FAQs
What is the difference between gross and adjusted flow?
Gross flow is the calculated or measured rate before losses. Adjusted flow applies your loss factor to better represent real delivery at the emitters, after friction, restrictions, and variability.
What loss factor should I start with?
Start with 8–12% for short hoses and simple zones. Use 15–25% for long runs, many fittings, regulators, or older tubing. Refine the value after a bucket test or zone observation.
How do I do a bucket test correctly?
Use a known container volume, open the valve to your normal setting, and time how long it takes to fill. Convert volume and time with the calculator, then repeat twice and average the results.
Can I size a drip zone using emitter ratings?
Yes. Count the emitters on the zone, multiply by the per‑emitter rating, and apply a loss factor. If emitters are pressure‑compensating, confirm the regulator pressure matches the rating.
Why does my flow change during the year?
Municipal pressure, pump performance, water temperature, and filter condition can shift flow. Summer demand often lowers supply pressure. Keeping exports helps you spot trends and schedule maintenance.
How do I use GPH to set a watering timer?
Decide the gallons you want to apply, divide by adjusted GPH to get hours, then convert to minutes. Recheck after system changes, and avoid running multiple zones at once if flow drops noticeably.