Amps to Watts Calculator (DC, AC, and Three-Phase)

To convert amps to watts, multiply the voltage by the current: watts equal volts times amps, often written volts x amps or amps x volts. For a DC or a purely resistive AC load, W = V × A. For other AC loads you also multiply by the power factor, and for three-phase you add a √3 factor. The one thing you always need is the voltage, because amps alone do not give watts.

Amps measure current, the flow of charge, and watts measure power, the rate at which energy is used. The voltage links them. A load pulling 10 A at 120 V draws 1,200 W, while the same 10 A at 12 V draws only 120 W, so the current is the same but the power is ten times higher at the higher voltage. For the kilowatt version of this conversion, the amps to kW calculator divides the result by 1,000.

Amps to Watts Formulas

Power factor and the three-phase factor only apply to AC. On DC and on resistive AC loads like heaters and incandescent bulbs, the power factor is 1 and drops out, so watts are just volts times amps. Motors, transformers, and electronics run at a power factor below 1, so their watts are lower than volts times amps alone would suggest. The volts-times-amps product before the power factor is the apparent power in volt-amperes; the amps to VA calculator covers that unit.

How to Use the Amps to Watts Calculator

1. Choose the current type: DC, AC single-phase, or AC three-phase.
2. Enter the current in amps and the voltage in volts. The default 120 V is the US household standard; use 240 V for large appliances or 12 V for automotive and solar.
3. For AC, enter the power factor (1 for resistive loads, about 0.8 to 0.9 for motors). For three-phase, pick line-to-line or line-to-neutral voltage.
4. Read the power in watts.

Amps to Watts Worked Examples

Example 1: 20 Amps at 120 V

A 20 A circuit at the US household voltage of 120 V carries:

W = 120 × 20 = 2,400 W

That is why a standard 20 A, 120 V circuit is often quoted at 2,400 W, and at a safe continuous 80 percent it is 1,920 W.

Example 2: 10 Amps at 240 V

A 10 A resistive load on a 240 V single-phase supply, where the power factor is 1:

W = 240 × 10 = 2,400 W

The same 2,400 W comes from half the current because the voltage is doubled. Higher voltage carries the same power at lower current.

Example 3: 30 Amps, Three-Phase at 208 V

A 30 A three-phase load at 208 V line-to-line and a 0.9 power factor:

W = 1.732 × 208 × 30 × 0.9 = 9,727 W

The √3 factor is what makes three-phase power different from single-phase at the same voltage and current.

Amps to Watts Conversion Chart

This chart gives the watts for common amp values at three US voltages, for DC or resistive loads where W = V × A. For an AC load with a power factor below 1, multiply by the power factor; for three-phase, multiply by √3 and the power factor.

Amps vs Watts: What's the Difference?

Amps and watts measure two different things: an amp is a unit of current, the rate that electric charge flows, and a watt is a unit of power, the rate that energy is used. Voltage connects them, through watts = volts × amps. You cannot convert amps to watts without knowing the voltage, which is why "how many watts in an amp" has no single answer. That amp vs watt difference comes down to current versus power.

A water analogy helps: current in amps is like the flow rate of water, voltage in volts is like the pressure pushing it, and power in watts is like the total work the moving water can do. A trickle at high pressure and a torrent at low pressure can carry the same power. In electrical terms, 1 A at 240 V and 2 A at 120 V both come to 240 W.

Amps are what a breaker or wire is rated for, because heat depends on current; watts are what a bill and an appliance rating are counted in, because they measure the actual power. This is also why a device's watts stay the same on 120 V or 240 V, but it pulls half the amps at the higher voltage. For the current-to-apparent-power view in volt-amperes, see the amps to kVA calculator.

How Many Watts Are in an Amp?

There is no fixed number of watts in an amp; it depends on the voltage. At the US household 120 V, 1 amp is 120 watts. At 240 V it is 240 watts, and at 12 V it is only 12 watts. The rule is watts = volts × amps, so one amp equals the voltage in watts for a DC or resistive load. So no, 1 amp is not 1,000 watts unless the voltage happens to be 1,000 V. Smaller currents work the same way, so converting milliamps to watts just means changing the milliamps to amps first (1,000 mA = 1 A) before multiplying by the voltage.

Amps to Watts at 120V, 240V, and 12V

The voltage in the formula is set by the system. In a US home, general circuits run at 120 V, so amps to watts uses 120: a 15 A circuit is 1,800 W. Large appliances like dryers, ranges, and EV chargers use 240 V, so the same current carries twice the watts. Automotive, RV, marine, and most solar and battery systems run on 12 V (or 24 V and 48 V) DC, where a 10 A draw is just 120 W. Outside North America, single-phase mains is usually 230 V, close to the US 240 V, so the watts per amp are similar.

Always use the actual voltage of your circuit. Using 120 V when the load is really on 240 V, or 12 V for a 120 V circuit, throws the watts off by the ratio of the voltages.

Three-Phase Amps to Watts

Three-phase power adds a √3 factor, so watts = √3 × volts × amps × power factor when the voltage is the line-to-line value. The √3, about 1.732, comes from the 120-degree phase spacing of the three lines. If you instead use the line-to-neutral voltage, the factor is 3 rather than √3, and the calculator handles both with the voltage-type selector.

Power factor matters most on three-phase because so many three-phase loads are motors. A 0.8 to 0.9 power factor is typical, and the real power in watts is that much lower than the volt-amperes. Apparent, real, and reactive power are defined in IEEE Std 1459, the standard for electric power quantities.

Amps to Watts for Generators, Batteries, and Solar

Amps to watts comes up whenever a nameplate lists one but you need the other. A load's amps times the voltage give the watts a generator has to cover, so a 30 A RV service at 120 V needs up to 3,600 W, and a 50 A RV service at 240 V up to 12,000 W. For batteries and solar the same rule holds: a 100 A draw from a 12 V battery is 1,200 W, and a solar panel putting out 8 A at 18 V is making about 144 W. Battery capacity in amp-hours converts to energy with the Ah to watts calculator.

Common Mistakes Converting Amps to Watts

• Forgetting the voltage. Amps alone do not give watts; you always need the voltage, because watts = volts × amps.
• Using the wrong voltage. A 120 V circuit and a 240 V circuit give very different watts for the same amps.
• Ignoring the power factor on AC. Motors and electronics draw fewer watts than volts times amps; multiply by the power factor.
• Leaving out the three-phase factor. Line-to-line three-phase power needs the √3 factor, or the watts come out too low.
• Confusing watts with volt-amperes. Volts times amps is the apparent power in VA; watts is the real power, which is VA times the power factor.

Disclaimer: This calculator converts current to power using the voltage, power factor, and phase you enter. Actual power and circuit sizing also depend on load type, continuous versus intermittent duty, and code rules such as the 80 percent continuous-load limit in the National Electrical Code (NFPA 70). Always verify against nameplate data and your local electrical code, and consult a licensed electrician for wiring, breaker, and load calculations.