When you need this conversion
Converting watts to amps comes up constantly in solar and home-electrical planning. You know a load's power rating in watts (a panel's output, an inverter's continuous rating, an appliance's label) but you need amps to size wire, pick a breaker, or check what a battery bank can actually deliver. Solar installers use it to size combiner-box fusing and inverter output conductors; homeowners use it to confirm an appliance will not overload a circuit.
The formula explained
Current in amps always equals power in watts divided by some combination of voltage and, for AC, power factor:
- DC circuits (solar panels, batteries): Amps = Watts ÷ Volts
- AC single-phase (most homes): Amps = Watts ÷ (Volts × Power Factor)
- AC three-phase (larger systems, commercial): Amps = Watts ÷ (√3 × Volts × Power Factor), where √3 is about 1.732
Power factor (PF) measures how much of the AC current actually does useful work. Purely resistive loads like heaters have a PF of 1. Motors, compressors, and some electronics run lower, often 0.8 to 0.95, which pulls more amps for the same wattage.
Common values at a glance
| Watts | Amps at 120V (PF 1) | Amps at 230V (PF 1) |
|---|---|---|
| 100 W | 0.83 A | 0.43 A |
| 500 W | 4.17 A | 2.17 A |
| 1000 W | 8.33 A | 4.35 A |
| 1500 W | 12.5 A | 6.52 A |
| 3000 W | 25.0 A | 13.04 A |
Practical tips
- Continuous loads running more than three hours, like solar arrays or EV chargers, should be sized at 125 percent of the calculated amps per standard electrical code practice.
- Motor-driven loads have inrush or surge current that can briefly hit five to seven times the running amps; breakers and inverters need headroom for that spike, not just the steady-state figure.
- Always confirm your actual voltage. Nominal 120V and 230V systems can sag or run high under load, which shifts the real amp draw.
- Wire gauge should be chosen from the ampacity, not the wattage directly, after applying any code derating for conduit fill, ambient temperature, or bundling.