About the Amps to Watts Calculator
Amps measure how much current flows, and watts measure how much power that current delivers, so converting between them always needs the voltage. This calculator multiplies the current by the voltage for a DC circuit, adds the power factor for single-phase AC, and uses the extra square root of three for three-phase AC. It gives you the power in watts and kilowatts, and for AC circuits it also shows the apparent power in volt-amperes and the reactive power. Use it to check what an appliance draws, to size a generator or inverter, or to work out whether a socket can cope with a load.
Updated October 2026
How to use the Amps to Watts Calculator
- 1Choose DC, single-phase AC or three-phase AC.
- 2Enter the current in amps.
- 3Enter the voltage. For three-phase, use the voltage between two lines.
- 4For AC, enter the power factor, such as 0.9 for a motor or 1 for a heater.
- 5Read the power in watts and kilowatts, with the apparent and reactive power below it.
Worked examples
A 12 volt car accessory that draws 8 amps uses 96 watts. A kettle taking 13 amps from a 230 volt supply uses about 2,990 watts, which is why it is rated at 3 kilowatts. A three-phase pump motor drawing 20 amps at 400 volts with a power factor of 0.85 delivers around 11.8 kilowatts of real power.
In each case the calculator shows the kilowatt figure too, which is what electricity bills use.
Typical voltages
- Cars and small solar systems: 12 or 24 volts DC.
- USB chargers: 5 volts DC.
- North American outlets: 120 volts AC.
- Most of Europe, Asia and Africa: 220 to 240 volts AC.
- Industrial three-phase: 208, 400 or 480 volts line to line.
Related electrical tools
Use the Watts to Amps Calculator for the opposite direction, the Ohm's Law Calculator to find resistance, the Voltage Drop Calculator to check long cable runs and the Power Factor Calculator for correcting motors. The Electricity Bill Calculator turns kilowatts and hours into cost.
Features
- DC, single-phase and three-phase formulas
- Power factor for AC loads
- Watts and kilowatts at once
- Apparent power in VA and reactive power in var
- Clear checks for impossible values
- Free and private
Frequently asked questions
What is the formula for converting amps to watts?
For DC, watts equal amps times volts. A 10 amp current at 12 volts is 120 watts. For single-phase AC, multiply by the power factor as well, so 10 amps at 230 volts and a power factor of 0.9 gives 2,070 watts.
Can I convert amps to watts without knowing the voltage?
No. Amps alone say how much current flows, not how much energy it carries. The same 10 amps is 120 watts at 12 volts but 2,300 watts at 230 volts. Look for the voltage on the device label or measure the supply.
What is power factor and why does it matter?
Power factor is the share of the supplied current that does useful work, a number between 0 and 1. Resistive loads like heaters have a power factor near 1, while motors and transformers are lower. A lower power factor means fewer real watts for the same amps.
How do I convert three-phase amps to watts?
Multiply the line current by the line-to-line voltage, by the square root of 3 (about 1.732) and by the power factor. At 10 amps, 400 volts and a power factor of 0.8 that gives about 5,543 watts.
What is the difference between watts and volt-amperes?
Watts are the real power that does work. Volt-amperes are the apparent power, voltage times current. They are equal when the power factor is 1 and differ for motors, which draw more apparent than real power.
Is this safe to use for choosing a cable or a fuse?
It is a good starting point, but cable and fuse choice also depends on the cable type, length, installation method and local regulations. Use the figures with the wiring rules in your country and ask a qualified electrician for fixed wiring.