When you need this conversion
Watts to volts conversion is less common than the other direction, but it matters whenever you know a load's power and a current limit and need to find the required voltage. This comes up when a wire gauge or fuse caps the amps a circuit can carry: knowing the wattage you need to deliver, you can work out the minimum voltage that keeps current under that limit, a common check in solar battery bank and DC wiring design.
The formula explained
Voltage equals power in watts divided by current in amps, adjusted for power factor on AC circuits:
Volts = Watts ÷ (Amps × Power Factor)
On DC systems, power factor is always 1, so voltage is simply watts divided by amps. On AC systems, a lower power factor means the same wattage requires more current at a given voltage, so solving for voltage at a fixed current produces a lower figure as PF drops.
Common values at a glance
| Watts | Amps | Volts required (PF 1) |
|---|---|---|
| 120 W | 10 A | 12 V |
| 240 W | 10 A | 24 V |
| 960 W | 20 A | 48 V |
| 1200 W | 10 A | 120 V |
| 2300 W | 10 A | 230 V |
Practical tips
- Use this calculation to check whether a 12V, 24V, or 48V battery bank can deliver a given wattage without exceeding your cable or breaker's amp rating.
- Higher system voltages let you deliver the same wattage at lower amps, which is why larger solar and battery systems often move from 12V to 24V or 48V architecture as power needs grow.
- Remember that this gives the required source voltage, not the voltage actually present at the load; voltage drop over cable length still needs to be checked separately.
- For AC circuits, confirm the real power factor of the load before relying on the result, since assuming PF equals 1 on inductive loads will understate the voltage needed.