Volts to Watts Calculator (AC & DC)

Convert volts (V) to watts (W) for DC, single‑phase AC, and three‑phase AC circuits. Use amps or ohms, include power factor, and see formulas and examples.

Volts to Watts Converter

Known values

How to convert volts to watts

Watts measure power, while volts measure electrical potential. To convert volts (V) to watts (W) you also need either current (amps) or resistance (ohms), and for AC circuits you must consider the power factor and phase configuration.

DC and single‑phase AC

Using current (amps)

DC or AC single‑phase:

$$P = V \\times I \\times PF$$

For DC and purely resistive AC loads, \(PF = 1\), so:

$$P = V \\times I$$

Using resistance (ohms) (Ohm's law)

$$P = \\frac{V^2}{R}$$

Three‑phase AC

Line‑to‑line voltage (most common):

$$P = \\sqrt{3} \\times V_{LL} \\times I \\times PF$$

Line‑to‑neutral voltage:

$$P = 3 \\times V_{LN} \\times I \\times PF$$

Example: 120 V, 10 A space heater

Heaters are nearly purely resistive, so PF ≈ 1.

  • Voltage \(V = 120\\,\\text{V}\)
  • Current \(I = 10\\,\\text{A}\)
  • Power factor \(PF = 1\)

Use \(P = V \\times I \\times PF\):

$$P = 120 \\times 10 \\times 1 = 1200\\,\\text{W}$$

Example: 230 V, 5 A, PF = 0.8 motor (single‑phase)

  • Voltage \(V = 230\\,\\text{V}\)
  • Current \(I = 5\\,\\text{A}\)
  • Power factor \(PF = 0.8\)

$$P = 230 \\times 5 \\times 0.8 = 920\\,\\text{W}$$

Example: 400 V three‑phase, 10 A, PF = 0.9

Assume 400 V is line‑to‑line voltage:

$$P = \\sqrt{3} \\times 400 \\times 10 \\times 0.9 \\approx 1.732 \\times 400 \\times 10 \\times 0.9 \\approx 6{,}235\\,\\text{W}$$

Volts to watts conversion table (DC or PF = 1)

Approximate power for common voltage and current combinations (DC or purely resistive AC):

Voltage (V) Current (A) Power (W)
5 2 10
12 5 60
24 10 240
120 5 600
120 10 1,200
230 5 1,150
230 10 2,300

Watts, volts, amps, and ohms at a glance

The four basic electrical quantities are related by Ohm’s law and the power equations:

  • V – volts (electrical potential)
  • I – amps (current)
  • R – ohms (resistance)
  • P – watts (power)

Ohm’s law:

$$V = I \\times R$$

Power formulas (DC / resistive AC):

$$P = V \\times I$$

$$P = I^2 \\times R$$

$$P = \\frac{V^2}{R}$$

FAQ

Can I convert volts to watts without amps?

Not uniquely. You must know at least one more parameter:

  • Resistance → use \(P = V^2 / R\)
  • Current → use \(P = V \\times I\)
  • For AC, also consider power factor and whether the system is single‑ or three‑phase.

What power factor should I assume?

  • Resistive loads (heaters, incandescent bulbs): PF ≈ 1.0
  • Small motors, transformers: PF ≈ 0.7–0.9 (0.8 is a common assumption)
  • Electronics with good power supplies: PF ≈ 0.9–0.99

What is the difference between watts and VA?

In AC circuits:

  • VA (volt‑amps) = apparent power = V × I
  • Watts (W) = real power = V × I × PF
  • Relationship: W = VA × PF

UPS units and transformers are often rated in VA, while loads are rated in watts.