About the Volts to Watts Converter
Volts on their own cannot be turned into watts — you also need either the current flowing (amps) or the resistance of the load (ohms). This volts to watts converter takes whichever you know and returns real power in watts and kilowatts, plus the current, resistance and apparent power (volt-amperes) that go with it.
Choose DC for batteries, solar panels and car electrics; single-phase AC for household outlets and appliances; or three-phase AC for motors, workshops and commercial supplies. For AC loads you can enter a power factor, because motors, compressors and power supplies draw current that is partly out of step with the voltage, so their real power is less than volts × amps.
For three-phase circuits enter the line-to-line voltage (for example 400 V or 480 V) and the line current; the tool applies the √3 factor automatically. When you work from resistance it assumes a purely resistive load such as a heater element.
With the default inputs, the real power is 1,200 W. Change any value above to recalculate instantly.
How to use the volts to watts converter
- 1Enter the supply or load voltage.
- 2Choose whether you know the current (amps) or the resistance (ohms) and enter it.
- 3For current, pick DC, single-phase AC or three-phase AC.
- 4For AC, enter the power factor from the nameplate (use 1 if unsure for heaters).
- 5Read the watts, kilowatts and the matching current and apparent power.
Formula and method
Electrical power is the rate at which energy is delivered, and in a DC circuit it is simply voltage multiplied by current. If you know resistance instead of current, Ohm’s law (I = V ÷ R) gives P = V² ÷ R, which assumes a purely resistive load.
In AC circuits volts × amps gives apparent power in volt-amperes (VA). Real power in watts is apparent power multiplied by the power factor, the cosine of the phase angle between voltage and current. For a balanced three-phase load measured line-to-line, apparent power is √3 (about 1.732) × V × I, because the three phases are 120° apart.
- P
- Real power in watts
- V
- Voltage in volts (line-to-line for three-phase)
- I
- Current in amperes
- R
- Resistance in ohms
- PF
- Power factor, 0 to 1 (1 for DC and resistive loads)
Worked examples
Small air compressor on a 230 V outlet drawing 5 A
230 V × 5 A = 1,150 VA of apparent power. A motor load like this has a power factor below 1; at 0.9 the real power is 1,150 × 0.9 = 1,035 W.
480 V three-phase motor at 20 A
√3 × 480 V × 20 A = 16,628 VA. Multiplying by a power factor of 0.85 gives 14,134 W, or about 14.1 kW of real power.
12 V across a 4 Ω speaker load
Current is 12 V ÷ 4 Ω = 3 A, so power is 12² ÷ 4 = 36 W (the same as 12 V × 3 A).
Frequently asked questions
How do I convert volts to watts?+
Multiply volts by amps: watts = volts × amps for DC or resistive loads. A 12 V device drawing 2 A uses 24 W. Without the current or the resistance, volts alone cannot be converted to watts.
How many watts is 120 volts?+
It depends on the current. At 120 V, 1 A is 120 W, 10 A is 1,200 W and a fully loaded 15 A circuit is 1,800 W. Continuous loads are normally kept to 80% of the breaker rating, about 1,440 W on a 15 A circuit.
How do I convert watts back to volts?+
Divide watts by amps: volts = watts ÷ amps. For example, 60 W at 0.5 A means 120 V. If you know resistance instead, volts = √(watts × ohms).
What is power factor and why does it matter?+
Power factor is the share of apparent power (volts × amps) that does real work. Heaters are close to 1, while motors and some power supplies run around 0.7–0.95. A low power factor means more current for the same watts.
Why does three-phase use √3?+
In a balanced three-phase system the three voltages are 120° apart. When you measure voltage between two lines, total power works out to √3 × V × I × PF, where √3 ≈ 1.732.