When you need this conversion
Amps to watts conversion shows up whenever you know a device's current draw but need its power rating instead. Solar charge controllers, battery bank fuses, and appliance nameplates are often labeled in amps, while inverter sizing, generator sizing, and energy calculations need watts. Knowing the wattage lets you compare loads directly, add them up for a total system draw, or check what a battery bank can support during peak demand.
The formula explained
Power in watts equals current in amps multiplied by voltage, adjusted for power factor on AC circuits:
- DC circuits (solar, batteries): Watts = Amps × Volts
- AC single-phase: Watts = Amps × Volts × Power Factor
- AC three-phase: Watts = √3 × Amps × Volts × Power Factor (√3 is about 1.732)
Power factor represents the share of current that performs real work. A PF of 1 means all the current converts to usable power; motors, pumps, and some electronics run lower, so the real wattage is less than amps times volts alone would suggest.
Common values at a glance
| Amps | Watts at 120V (PF 1) | Watts at 230V (PF 1) |
|---|---|---|
| 5 A | 600 W | 1150 W |
| 10 A | 1200 W | 2300 W |
| 15 A | 1800 W | 3450 W |
| 20 A | 2400 W | 4600 W |
| 30 A | 3600 W | 6900 W |
Practical tips
- Nameplate amp ratings on appliances often reflect the maximum draw, not typical running current, so real-world wattage can run lower than the calculated figure.
- For AC loads, use the actual power factor when you know it. Assuming PF equals 1 on a motor or compressor will overstate the true wattage.
- When sizing an inverter or generator from amp-rated loads, add up total watts across everything that runs at once, not just the largest single load.
- For battery-based solar systems, use the pack's nominal voltage (12V, 24V, or 48V) rather than a charging voltage, for a realistic average wattage estimate.