amps to watts

W = V × I. Power needs two quantities, so current becomes watts only when the voltage is known: 10 A at 120 V is 1,200 W, but the same 10 A at 240 V is 2,400 W. Substituting Ohm’s law gives W = I² × R.

The watts a device consumes are its current multiplied by the circuit voltage: P = V·I. A 15 A space heater on a 120 V circuit burns 1,800 W; the same 15 A on a 240 V dryer circuit burns 3,600 W. This calculator converts the current you read on a clamp meter into the power you pay for on the bill.

By EnginStack Editorial Team | Reviewed against NIST, BIPM and primary-source documentation About →
amps
volts
— watts
— —

Verified against NIST Special Publication 811 and BIPM SI definitions. The conversion factor is exact and traceable to the 1959 treaty constants.

amps to watts

Appliance ratings are quoted in watts, but the circuit that feeds them is protected in amps — so every load calculation converts one to the other. The 120/240 split in US homes makes the voltage the key input: the same 15 A breaker feeds twice the power at 240 V. For resistive loads this is exact; for motors, multiply by the power factor. The watts result then flows into energy billing via kilowatt-hours, which is where the energy family takes over.

watts = amps × volts
P = V·I
Exact watt's law — the product of the current and voltage you provide.

Worked Examples

Example 1: Convert a 15 A heater on a 120 V circuit

15 × 120 = 1,800 W

Example 2: Convert a 30 A dryer circuit on 240 V

30 × 240 = 7,200 W

Example 3: Convert a 10 A load on 12 V

10 × 12 = 120 W

Common amps to watts Values

ampsvoltswattsContext
15 A120 V1,800 WSpace heater, full load.
15 A240 V3,600 WElectric dryer.
5 A120 V600 WMicrowave.
10 A12 V120 WAutomotive accessory.
30 A240 V7,200 WRange circuit.

Engineering Context

Amps-to-watts is the mirror of watts to amps — P = V·I versus I = P/V. Both feed the energy hub: watts become kilowatt-hours on your bill via watts to kW and Wh to kWh. The electric hub collects all twelve electric converters.

Multiplying current by voltage gives real power only when the current and the voltage are in phase, which for a resistive load such as a heater they are. Motors, transformers and electronic supplies draw a current that is shifted relative to the voltage, so their product overstates the power actually converted to work. The correct figure is volts times amperes times the power factor, and the difference between the two is billed as volt-amperes, which is why industrial tariffs charge for reactive demand separately. A motor drawing fifteen amperes at two hundred and forty volts with a power factor of 0.85 draws 3.6 kVA but supplies only about 3.06 kilowatts of mechanical and thermal output, and the gap is real energy moving back and forth rather than being consumed.

More: W to A · V to W · A to V · Electric Guide · Electric Hub

Related Unit Converters

watts to amps volts to watts amps to volts Electric Conversion Guide Electric Converters

Frequently Asked Questions

How do I convert amps to watts?

Multiply amps by volts: P = V·I. A 15 A heater on 120 V uses 1,800 W. For motors and inductive loads, multiply by the power factor as well.

Why does the same 15 amps give different watts on different circuits?

Because power is voltage times current. 15 A at 120 V is 1,800 W; 15 A at 240 V is 3,600 W. The US dual-voltage system is exactly why dryers and ranges are wired for 240 V.

What can I run on a 15-amp circuit?

At 120 V, up to 1,800 W (the 80% rule suggests staying under 1,440 W continuous). This calculator converts your appliance's watts to the amps it will draw so you can check the breaker.