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Amps to Watts Calculator

Convert amps to watts with our free amps to watts calculator. Enter the current in amps and the voltage, and it works out the power in watts — 10 amps at 120 volts is 1,200 watts. Flip the direction to turn watts back into amps.

Common appliances

How it works

Amps, volts, and watts are three ways of describing the same electricity. Volts measure electrical pressure — how hard the power pushes. Amps measure current — how much electricity actually flows. Watts measure power — how much work the electricity does each second. The three are tied together by Watt's law: watts equals amps times volts. Raise the current or raise the voltage, and the power goes up by the same amount.

A helpful picture is water in a pipe. Voltage is the water pressure, current is how much water flows, and power is how much work the water can do when it reaches a wheel. A thin stream at high pressure and a wide stream at low pressure can do the same work, just as 10 amps at 120 volts and 5 amps at 240 volts both give 1,200 watts. That is why large appliances in many homes run on 240 volts: the same power needs half the current, so the wires can be thinner and run cooler.

To convert amps to watts, multiply amps by volts. To go the other way, divide watts by volts. For example, 10 A × 120 V = 1,200 W, and 1,500 W ÷ 120 V = 12.5 A. The calculator above does both directions — pick one in the menu and it relabels the input for you. One kilowatt is 1,000 watts, so a 1,500 W heater is a 1.5 kW heater, and running it for one hour uses 1.5 kilowatt-hours of energy.

This math is what keeps a circuit safe. A standard household circuit with a 15-amp breaker can carry 15 × 120 = 1,800 watts before it trips, and electricians recommend staying under 80 percent of that — about 1,440 watts — for anything that runs a long time. That is why a 1,500-watt space heater plus a 1,200-watt microwave on the same circuit is a problem: together they draw 2,700 watts, or 22.5 amps, and the breaker trips. Add up the watts on a circuit before you plug in a second big appliance, and you will know the answer before the lights go out. This calculator gives planning numbers only — for any real wiring work, hire a licensed electrician.

Worked example

Lisa has a space heater rated at 1,500 watts, and she wants to know how many amps it draws on her 120-volt circuit so she can check whether it is safe to run with anything else plugged in.

Step 1: Write down the power — 1,500 W.
Step 2: Write down the voltage — 120 V.
Step 3: Divide: 1,500 ÷ 120 = 12.5.
Step 4: Read the answer — 12.5 amps.

That is the exact result this calculator gives for 1,500 W at 120 V: 12.5 A. On a 15-amp circuit that is 83 percent of the breaker's capacity, above the 80 percent guideline for continuous loads — so Lisa should run the heater alone on that circuit. Going the other way, 10 A × 120 V = 1,200 W, which is the draw of a typical microwave.

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