Watts to Amps Calculator

This calculator converts power in watts to current in amperes for both DC and single-phase AC circuits. Knowing the current a device draws is essential for selecting the right fuse, circuit breaker, cable size, or extension lead. For a DC circuit the formula is straightforward: I = P divided by V, where I is current in amps, P is power in watts, and V is voltage in volts. For an AC circuit you also need the power factor (PF), which accounts for the phase difference between voltage and current caused by inductive or capacitive loads. The AC formula is I = P divided by (V times PF). A purely resistive load such as a kettle or incandescent bulb has a power factor of 1.0, so the DC and AC results are the same. Motors, fluorescent lighting, and switch-mode power supplies typically have a power factor between 0.7 and 0.95, meaning they draw more current than the watt figure alone suggests. You enter the power in watts, the supply voltage, and the power factor, and the calculator returns the current in amps, the apparent power in volt-amps, and the reactive power in VAR. Select DC mode to ignore the power factor entirely. For the default example of 2,400 W at 240 V with PF 1.0, the current is 10.00 A. These results are for single-phase AC only; three-phase calculations use a different formula and are outside the scope of this tool.

Circuit type

Power (P)

Voltage (V)

Power factor (PF)

10.00 A

current

Apparent power2400.00 VA

Reactive power0.00 VAR

How it works

For DC or AC with PF = 1.0: I = P divided by V. For single-phase AC: I = P divided by (V times PF). Apparent power (VA) is V times I. Real power (W) equals apparent power times PF. Reactive power (VAR) is the square root of (VA squared minus W squared). Power factor must be between 0 and 1; a value of 1.0 means the load is purely resistive. Division by zero is caught and flagged.

Worked example

An AC circuit supplies 2,400 W at 240 V with a power factor of 1.0. Current = 2400 divided by (240 times 1.0) = 10.00 A. Apparent power = 240 times 10 = 2,400 VA. Reactive power = 0 VAR because PF = 1.0. These match the default values pre-filled above.

Related calculators

Amps to Watts Calculator: the reverse conversion from current and voltage to power.
Ohm's Law Calculator: solve for voltage, current, or resistance using V=IR.
Electrical Power Calculator: find power using any two of voltage, current, and resistance.
Percent Error Calculator: check how close your current readings are to calculated values.

Frequently asked questions

How do I convert watts to amps?

For a DC circuit, divide power in watts by voltage in volts: I = P divided by V. For a single-phase AC circuit, you also divide by the power factor: I = P divided by (V times PF). The power factor accounts for reactive loads such as motors and fluorescent lights, which draw more current than the real power alone would suggest.

What is a power factor and why does it matter?

Power factor (PF) is the ratio of real power (watts) to apparent power (volt-amps). A purely resistive load like an electric heater has PF = 1.0. Motors, transformers, and switch-mode power supplies typically have a PF between 0.7 and 0.95. A lower power factor means more current is drawn for the same useful power, which matters when sizing cables and circuit breakers.

How many amps does a 2400 W appliance draw on 240 V?

At unity power factor (PF = 1.0), a 2,400 W appliance on a 240 V circuit draws I = 2400 divided by (240 times 1.0) = 10.00 A. If the power factor is 0.9, the current rises to 2400 divided by (240 times 0.9) = 11.11 A.