Enter your equipment and circuit details
Example data table
| Scenario | Loads | Voltage | PF | Efficiency | Estimated current |
|---|---|---|---|---|---|
| Grow tent lighting | 2 × 300 W LED | 230 V (AC) | 0.95 | 0.90 | ≈ 3.05 A |
| Irrigation pump | 1 × 750 W pump | 230 V (AC) | 0.85 | 0.88 | ≈ 4.47 A |
| Solar aerator | 1 × 120 W DC load | 24 V (DC) | — | 0.92 | ≈ 5.43 A |
Formula used
- DC current: I = P / (V × η)
- Single-phase AC current: I = P / (V × PF × η)
- Three-phase AC current: I = P / (√3 × VLL × PF × η)
- Breaker target: continuous ≈ 1.25 × I, otherwise ≈ 1.10 × I
P is total watts of all devices. η is efficiency (0–1).
How to use this calculator
- Select AC or DC and choose phase.
- Enter voltage from your supply or inverter.
- Enter power factor and efficiency for AC loads.
- Add each device with quantity and watts.
- Click Calculate to view amps and breaker guidance.
- Download CSV or PDF for job notes and checks.
For motors, use nameplate watts when possible. If only horsepower is known, convert first. Always confirm final sizing with local electrical rules.
Load characterization for garden circuits
Garden electrical planning starts with an accurate load list. Add pumps, aerators, grow lights, heaters, timers, and chargers, then multiply by quantity. Use nameplate watts when available. If only volts and amps are shown, compute watts as V × A for DC, or V × A × power factor for AC. Group loads by location so you can decide whether one circuit serves a bed, a greenhouse bay, or a pond station.
Power factor and motor behavior
Induction motors and some LED drivers draw current that does not align with voltage. Power factor captures that mismatch, and lower values raise amperage for the same real watts. For garden pumps, power factor can vary with loading and control type. Using a realistic range improves breaker selection and reduces nuisance trips when the pump starts or when multiple loads switch on together.
Efficiency and real input power
Efficiency bridges the gap between useful output and electrical input. A pump rated at 750 W output may require more input power depending on efficiency. Entering efficiency lets the calculator estimate the current your wiring actually sees. When efficiency is unknown, use a conservative value so the current estimate stays on the safe side, especially for older motors, small compressors, and mixed loads on extension runs.
Continuous operation and breaker margin
Many garden systems run for long periods, such as irrigation cycles, hydroponic circulation, or winter frost protection. Continuous operation increases conductor heating and demands more margin. The calculator applies a higher multiplier for continuous duty, then rounds to a common breaker size. Treat the breaker value as a planning target, not a substitute for code checks on conductor temperature rating, bundling, and ambient heat.
Using results for planning expansions
Once you have amperage, compare it with available circuit capacity and add headroom for future upgrades. If the suggested breaker is close to an existing rating, consider splitting loads, adding a dedicated circuit, or moving high draw equipment to a separate supply. Save CSV for job notes and PDF for inspections or contractor discussions. Recalculate when you change voltage, add devices, or switch to a three‑phase pump.
FAQs
What inputs matter most for accurate amperage?
Voltage and total watts drive the result. For AC, power factor and efficiency can change current noticeably, especially with motors. Use nameplate data when possible, and avoid guessing low margins for safety.
How do I estimate watts when only horsepower is listed?
Convert horsepower to watts, then adjust for efficiency. A common starting point is 1 hp ≈ 746 W output. Divide by efficiency to estimate input watts, then apply power factor for AC if needed.
Should I include starting or surge current for pumps?
This calculator focuses on running current. Motors can draw higher current at startup. If your pump starts under load, consider additional margin, soft start, or a dedicated circuit to reduce nuisance tripping.
Why does three‑phase show lower current for the same watts?
Three‑phase power delivers the same real watts with current shared across phases. The √3 term in the formula reflects that relationship. Use line‑to‑line voltage for the three‑phase option.
Can I use this for solar and battery systems?
Yes. Select DC, enter your system voltage, and use efficiency to account for inverter or controller losses. For long cable runs, also check voltage drop and conductor heating separately.
Is the wire size hint a final recommendation?
No. It is a quick planning guide only. Final sizing depends on local code, insulation temperature rating, installation method, bundling, ambient temperature, and allowable voltage drop for your equipment.