Amps to Watts Calculator

Converting amps to watts tells you how much real power a circuit carries at a given voltage and current. Breakers and wire are rated in amps; appliances and energy bills use watts—this tool bridges the two.

Enter current in amps, select system voltage (12/24/48 V DC or 120/230 V AC), and set power factor. For DC and resistive AC loads, power factor is 1. For motors and other inductive equipment, use a PF below 1 so watts reflect real power, not apparent power.

Use the result to estimate load on an inverter, compare circuit capacity to appliance demand, or translate clamp-meter amp readings into watts. Pair with the watts-to-amps calculator for the reverse direction.

How this calculator works

1. Enter current in amps—steady-state or maximum draw on the circuit.
2. Select voltage: 12, 24, or 48 V for DC battery systems; 120 or 230 V for AC mains.
3. Set power factor: 1.0 for DC and resistive loads; 0.7–0.95 for typical motors if known.
4. DC formula: watts = amps × volts.
5. AC formula: watts = amps × volts × power factor. Output is real power in watts.

Core conversion relationships

DC: P = I × V | AC: P = I × V × PF | P = watts, I = amps, V = volts, PF = power factor

Power is the product of voltage and current in DC. On AC, the product of volts and amps gives apparent power (VA) unless you include power factor—real watts = volts × amps × PF. Unity power factor means current and voltage are in phase, typical of heaters and incandescent bulbs.

Formulas used by this tool

• DC: watts = amps × volts.
• AC: watts = amps × volts × power factor.
• Use your circuit voltage and applicable power factor.

Worked example: 12.5 A at 120 V

A clamp meter reads 12.5 A on a 120 V AC resistive circuit (power factor 1.0).

1. Watts = 12.5 A × 120 V × 1.0 = 1,500 W real power.
2. That matches a typical 1,500 W space heater on a 15 A circuit.
3. On 12 V DC at 12.5 A: watts = 12.5 × 12 = 150 W—same current, ten times less power at lower voltage.
4. If the load were a motor at PF 0.8: watts = 12.5 × 120 × 0.8 = 1,200 W real, even though apparent VA is 1,500.

Practical tips

• Clamp meters often read RMS amps—pair with voltage and PF for watts, not VA alone on AC.
• For DC battery loads, amps × volts gives power directly at the bus voltage.
• Sum individual load watts after conversion when planning inverter or generator capacity.
• Motor starting current is higher than running amps—do not use surge amps for steady watt estimates.
• Lower PF means fewer real watts for the same amp draw—important for generator and UPS sizing.

Frequently asked questions

Related guides

• Electrical Basics: Watts, Amps, kWh, and Circuit Limits