Volts to Watts | Electrical Calcs

How to convert volts to watts (you need amps)

Here's the catch most quick answers skip: volts alone can't give you watts. Watts is power, and power is volts times amps — so you always need the current too. Once you have both, it's simple:

System	Formula	Example
DC	W = V × A	12 V × 10 A = 120 W
AC single-phase	W = V × A × PF	120 V × 10 A = 1200 W
AC three-phase	W = √3 × V × A × PF	480 V × 10 A = 8314 W

For DC and simple resistive loads the power factor is 1.0, so watts are just volts × amps. To get kilowatts, divide the watts by 1000.

Don't have the amps? Use Ohm's law

If you know the resistance instead of the current, get the amps first with Ohm's law — amps = volts ÷ ohms — then multiply by volts. For a purely resistive load that also works in one step as watts = volts² ÷ ohms. Example: 120 V across 24 Ω is 5 A, or 600 W (120² ÷ 24).

Power factor and three-phase

On AC, the real power in watts is volts × amps × power factor. Resistive loads (heaters, incandescent bulbs) are power factor 1.0; motors and other reactive loads run around 0.8, which lowers the watts for the same volts and amps. Three-phase adds a √3 (about 1.732):

Power factor in action

120 V × 12 A:
• at PF 1.0 (resistive) → 1440 W
• at PF 0.8 (motor) → 1152 W of real power
And a three-phase example: 480 V × 10 A × 1.0 → 8314 W (8.31 kW).

Volts to watts for 12V and 24V (solar & batteries)

On DC systems — cars, RVs, solar arrays, and battery banks — there's no power factor, so watts are simply volts × amps. That's why a 12 V × 10 A load is 120 W, and a 24 V × 10 A load is 240 W. It also works in reverse: a 100-watt solar panel at 12 V pushes about 8.3 amps (100 ÷ 12), which is why higher-voltage systems carry the same power on smaller wire.

DC system	Current	Watts
12 V	5 A	60 W
12 V	10 A	120 W
24 V	10 A	240 W
48 V	10 A	480 W

Volts to watts chart

Common voltages times a few sample currents, at power factor 1.0 (single-phase / DC):

Voltage	× 5 A	× 10 A	× 20 A
12 V	60 W	120 W	240 W
24 V	120 W	240 W	480 W
120 V	600 W	1200 W	2400 W
240 V	1200 W	2400 W	4800 W

For three-phase, multiply any of these by √3 (1.732) — so 480 V × 20 A three-phase is about 16,628 W (16.6 kW).

From watts to the circuit (and to kW)

Watts divided by 1000 gives kilowatts (4800 W = 4.8 kW). To size the circuit, work from the amps — and remember the NEC 125% rule for continuous loads (running three hours or more). If you started from a power rating instead, the kW to amps calculator gets you back to current, and the Wire Size Calculator and Breaker Size Calculator finish the job. The AWG ampacity chart has the conductor ratings.

Frequently asked questions

ConversionsHow do you convert volts to watts?

Multiply volts by amps: watts = volts × amps. For AC, multiply by the power factor, and for three-phase also multiply by √3. You always need the current, not just the voltage.

⚡ Size the circuit →

ConversionsCan you convert volts to watts without amps?

No. Watts is power, which equals volts times amps, so you need both the voltage and the current. Volts alone is not enough to find watts.

ConversionsHow many watts is 120 volts?

It depends on the current. At 120 volts, 10 amps is 1200 watts and 15 amps is 1800 watts. Multiply the volts by the amps to get the watts.

ConversionsHow many watts is 12 volts?

At 12 volts, watts equal 12 times the current — so 12 V × 10 A is 120 watts. This DC math is common for cars, RVs, solar panels, and batteries.

ConversionsWhat is the volts to watts formula?

P = V × I × PF for single-phase AC, √3 × V × I × PF for three-phase, and simply V × I for DC (power factor 1.0).

ConversionsHow do I convert volts to watts for three-phase?

Watts = √3 × volts × amps × power factor, using the line-to-line voltage. For example, 480 V × 10 A at PF 1.0 is about 8314 watts.

ConversionsDoes power factor affect watts?

Yes, on AC. Real power in watts equals volts × amps × power factor, so a lower power factor gives fewer real watts for the same volts and amps. DC has no power factor.

ConversionsHow do I convert watts to kW?

Divide the watts by 1000. So 4800 watts is 4.8 kilowatts, and 1200 watts is 1.2 kW.

Dr. Artie Vance

Technical reviewer · Ph.D. in Physics, MIT · 14 years' experience · Formulas verified against IEEE / NEC conventions

This calculator gives estimates from the standard power formula. Real AC loads vary with power factor, and circuit sizing follows the NEC and your local authority having jurisdiction (AHJ). When in doubt, hire a licensed electrician.