Amps to Watts Calculator

The Amps to Watts Calculator converts electric current (in amperes) into power (in watts) for DC, AC single-phase, and AC three-phase circuits. Beyond the raw wattage, it breaks your load down into real power (W), apparent power (VA), and reactive power (VAR), and draws them on an animated power triangle so you can see exactly how power factor turns current into useful work.

How to Convert Amps to Watts

The conversion depends on whether the circuit is DC or AC, and for AC, on the power factor of the load.

Where P is real power in watts, V is voltage in volts, I is current in amps, and PF is the power factor (a number between 0 and 1). For a purely resistive load the power factor is 1, so the AC formula reduces to the same volts × amps as DC.

Why You Always Need Voltage

Amps measure how fast electric charge flows; watts measure power, the rate at which energy is used. Power is the product of "push" (voltage) and "flow" (current), so you cannot turn amps into watts without knowing the voltage. This is why every honest amps-to-watts calculator asks for a voltage — a bare current value simply doesn't contain enough information.

Watts vs VA vs VAR: The Power Triangle

In AC circuits with motors, transformers, or other inductive loads, not all the current does useful work. Engineers split power into three related quantities that form a right triangle:

• Real power (P, watts) — the power that actually does work, such as heating, lighting, or turning a shaft. This is the "watts" most people mean.
• Apparent power (S, volt-amps / VA) — the total product of voltage and current that the wiring and supply must carry, whether or not it does useful work.
• Reactive power (Q, volt-amps reactive / VAR) — power that sloshes back and forth between the source and the load's magnetic or electric fields without doing net work.

The phase angle φ = arccos(PF) is the corner angle of the triangle. A power factor near 1 gives a thin, almost flat triangle (nearly all real power); a low power factor gives a tall triangle with lots of wasted reactive power.

Amps to Watts Conversion Chart (at Power Factor 1)

For DC or resistive AC loads, watts = volts × amps. For inductive AC loads, multiply by the power factor to get real power.

Typical Power Factors

• 1.0 — resistive loads: incandescent bulbs, electric heaters, kettles, toasters.
• 0.9 – 0.95 — modern electronics with power-factor correction, LED lighting.
• 0.8 – 0.9 — running electric motors, pumps, and fans.
• 0.4 – 0.6 — lightly loaded or starting motors, some older fluorescent ballasts.

How to Use This Calculator

1. Choose the current type: DC, AC single-phase, or AC three-phase.
2. Enter current and voltage: Type the current in amps and the voltage in volts. For three-phase, use the line-to-line voltage.
3. Enter the power factor: For AC, enter a value between 0.1 and 1.0 (leave the default 0.9 if unsure). It is hidden for DC.
4. Click Calculate: See the real power in watts, the apparent and reactive power, the animated power triangle, and everyday examples of what the wattage can run.

Frequently Asked Questions

How do you convert amps to watts?

For a DC circuit, watts equal volts times amps: P = V × I. For AC single-phase, multiply by the power factor: P = V × I × PF. For AC three-phase, use P = √3 × V × I × PF, where V is the line-to-line voltage. You always need the voltage to convert amps to watts.

Why do I need voltage to convert amps to watts?

Amps measure the rate of electric charge flow, while watts measure power, which is the rate of energy use. Power depends on both current and the voltage pushing that current, so watts = volts × amps. Without the voltage, current alone cannot tell you the power.

What is power factor and why does it matter?

Power factor is the ratio of real power (watts, the part that does useful work) to apparent power (volt-amps, the total the circuit carries). It ranges from 0 to 1. Resistive loads such as heaters have a power factor near 1, while motors and other inductive loads are often 0.8 to 0.9, meaning some current does no useful work.

What is the difference between watts, VA, and VAR?

Watts (W) are real power that does useful work. Volt-amps (VA) are apparent power, the total product of voltage and current. Volt-amps reactive (VAR) are reactive power that flows back and forth without doing work. They relate through the power triangle: apparent power squared equals real power squared plus reactive power squared.

How many watts is 10 amps at 120 volts?

At a power factor of 1 (a resistive load), 10 amps at 120 volts is 1,200 watts (120 × 10). If it is an AC load with a power factor of 0.9, the real power is 1,080 watts, while the circuit still carries 1,200 VA of apparent power.

Do I use line-to-line or line-to-neutral voltage for three-phase?

The three-phase formula P = √3 × V × I × PF uses the line-to-line voltage (for example 400 V or 480 V). The √3 factor already accounts for the three phases, so you should not also switch to the line-to-neutral voltage.

Additional Resources

• AC Power - Wikipedia
• Power Factor - Wikipedia