Inputs for pump runtime and cost
Formula used
- By Volume: convert chosen unit to liters.
- By Area & Depth: Volume (L) = Area (m²) × Depth (mm).
- Total runtime (minutes) = Volume (L) ÷ Effective Flow (L/min)
- Per-zone runtime (minutes) = Total runtime ÷ Zones
- Energy per run (kWh) = Power (W) × Runtime (hours) ÷ 1000
- Cost per run = Energy per run × Rate
- Weekly totals multiply by Runs per week
How to use this calculator
- Pick a water demand method. Use By Volume if you already know liters/gallons. Use By Area & Depth for irrigation planning.
- Enter your pump flow in any supported unit. For best accuracy, measure real flow at the hose/bib.
- Set efficiency and losses. If filters clog or hoses leak, raise losses or lower efficiency.
- If your pump struggles on elevation or long runs, enable head derating and enter heads. This reduces flow when actual head is higher than rated head.
- Add zones and weekly runs to see per-zone minutes and weekly energy cost.
- Click Calculate Runtime. Use the export buttons to save a log.
Water Demand
Use either a known tank volume or an area-and-depth estimate to define watering demand. Converting to liters keeps results consistent. The area method follows a rule: one millimeter applied over one square meter equals one liter. This translates target soil wetness into a number. Start with conservative depths, then adjust. For drip systems, use longer soak times to limit runoff.
Flow Adjustments
Pump labels often show optimistic flow. This calculator applies two realism controls: overall efficiency and estimated losses. Efficiency reflects wear, voltage, and pump curve behavior, while losses capture leaks, filter restriction, and friction. Many garden setups land between 70–90% efficiency and 5–25% losses, depending on hose length and emitter type. If your sprinklers look weak, reduce efficiency or raise losses.
Head Effects
Elevation and pressure requirements reduce delivered flow. When head derating is enabled, the calculator applies a head factor once actual head exceeds the rated head. Rated head is where your listed flow is expected; max head approximates shutoff. As actual head moves toward max, usable flow is reduced, protecting runtime from being underestimated. Measure static lift, then add expected friction for pipes and fittings.
Zone Scheduling
Zone planning matters because most gardens cannot irrigate every line at once. Enter the number of zones to see minutes per zone, assuming each zone shares the total demand equally. If zones differ, run the calculator per zone using separate volumes or areas. Use runs per week to build a repeatable schedule, balancing deeper, less frequent watering with lighter, frequent cycles during heat.
Energy Costs
Energy estimates turn runtime into operating cost. The calculator converts minutes to hours, multiplies by pump wattage, then reports kilowatt-hours and cost per run using your rate. Track weekly totals to compare seasonal changes, nozzle upgrades, or filter maintenance. Small adjustments—shorter hoses, clean filters, correct emitter pressure—can improve effective flow and lower runtime, often saving both water and electricity. Record results monthly to spot performance drift and maintenance needs.
FAQs
How do I measure real pump flow?
Fill a bucket of known volume and time it. Convert to liters per minute, then enter that value with the matching unit. Repeat twice and average for better stability.
What efficiency and loss values are reasonable?
Start with 85% efficiency and 10% losses for a short hose and clean filter. For long runs, small emitters, or clogged filters, drop efficiency or increase losses until the calculated runtime matches observed watering.
When should I use head derating?
Enable it if you pump uphill, use long piping, or require pressure for sprinklers. Use rated head from your pump curve, max head as shutoff, and actual head as lift plus friction and pressure.
How do I calculate for different zones?
If zones differ, run the calculator per zone. Use each zone’s area and depth (or target liters) and the same pump settings. The per-zone minutes will be more realistic than splitting total demand evenly.
Why does the effective flow look low?
Losses, low efficiency, or high head can reduce delivered flow sharply. Check for leaks, clean filters, shorten hoses, and verify that sprinklers are not demanding more pressure than your pump can provide.
Can I use it for filling a tank or pond?
Yes. Choose the volume method and enter the tank or pond fill volume. If you know the flow at the outlet, the calculator will estimate fill time and energy per fill using your pump power.
Example data
| Scenario | Water demand | Pump flow | Efficiency / Losses | Zones | Estimated total runtime |
|---|---|---|---|---|---|
| Raised beds top-up | 300 L | 20 L/min | 85% / 10% | 1 | ~19.6 min |
| Lawn soak | Area 40 m², depth 8 mm (≈320 L) | 18 L/min | 80% / 12% | 2 | ~25.3 min |
| Drip zones with head limits | 600 L | 30 L/min | 85% / 15% + head derating | 3 | ~30–45 min |