Mobile & Electronics

Watt to Amp Calculator

How many amps a given wattage draws at a given voltage - the figure that decides whether a circuit copes.

5 inputs Free, no sign-up

Your figures

From the appliance's rating plate.

The supply voltage. Mains in India is nominally 230 V; USB is 5 V unless a fast-charge mode has negotiated something higher.

Leave at 1 for DC and for resistive loads such as a heater or a kettle. Motors, pumps and air conditioners are lower, and their rating plate says so - at 0.8, the same wattage draws 25% more current.

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Result

Your result

Enter your figures and the result appears here.

Estimates only. Rates, fees and specifications change. Confirm against the official source before you rely on a figure — see our disclaimer.

About this calculator

Watts do not tell you how much current something draws — the voltage does that too. A 1,000 W appliance draws about 4.3 A on a 230 V mains supply and about 200 A at 5 V, which is why the same wattage means something completely different on a wall socket and on a USB port.

Current is what matters for cables, fuses and breakers. A circuit trips on amps, not on watts, so this is the conversion to do before deciding whether an extension lead will cope.

How to use this calculator

  1. Enter the power from the appliance's rating plate, in watts or kilowatts.
  2. Enter the supply voltage — 230 V for Indian mains, 5 V for a basic USB port, or whatever your supply is rated at.
  3. For a motor, a pump or an air conditioner, set the power factor from its rating plate. It matters: at 0.8 the same wattage pulls a quarter more current than at 1.

The formula

Current = Power / Voltage                    DC, or resistive AC
Current = Power / (Voltage x Power factor)   AC with a power factor

The power factor is not a detail that can be ignored on inductive loads. A 1,000 W motor at a power factor of 0.8 draws 5.4 A on 230 V, not 4.3 A — a 25% difference, and enough to matter when sizing a cable or a breaker.

SymbolMeaningUnit
P Power from the rating plate W
V Supply voltage V
pf Power factor
I Current drawn A

Worked example

A 1,000 W microwave on a 230 V supply:

I = 1000 / 230 = 4.35 A

The same 1,000 W as a motor with a power factor of 0.8:

I = 1000 / (230 x 0.8) = 5.43 A

Notes and limits

  • Size cables and breakers on current, never on wattage, and allow for the surge when a motor or a compressor starts — it is several times the running current for a moment.
  • Mains voltage in India is nominally 230 V but varies in practice. A lower supply voltage means a higher current for the same power, so a nominal figure is a starting point.
  • The rating plate usually gives the maximum. A device drawing less than its rating is normal.
  • This is single-phase. Three-phase has an additional root-three factor.
  • This is arithmetic, not electrical advice. Wiring, fusing and earthing are work for a qualified electrician.

What this calculation assumes

  • Single-phase supply; three-phase needs an additional root-three factor.
  • A power factor of 1 treats the load as DC or purely resistive.
  • The wattage entered is the running power, not the surge when a motor starts.

Frequently asked questions

How many amps is 1,000 watts?

It depends entirely on the voltage. On a 230 V Indian mains supply, about 4.35 A. At 12 V, about 83 A. At 5 V, about 200 A. Watts alone do not give amps.

Do I need the power factor?

For a heater, a kettle or an incandescent bulb, no - those are resistive and the power factor is effectively 1. For a motor, pump, air conditioner or older fluorescent fitting, yes, and it is on the rating plate. Ignoring it understates the current.

What size cable or fuse do I need?

That is more than a current figure. It depends on the cable length, how it is installed, the ambient temperature, the type of protection and the wiring rules that apply. Use this to know the current, then ask a qualified electrician.

Why is my measured current higher than this?

The usual reasons are a power factor below 1 that was not allowed for, a supply voltage below nominal, or a starting surge on a motor. Measured current above the rating plate on a steady load is worth investigating.

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