Watts to Amps Calculator
Convert electrical power in watts to current in amps for a DC, single-phase AC or three-phase AC circuit. Choose the circuit type, set the voltage and power factor, and the calculator returns the current in amps and milliamps, shows the full working, and can estimate the running cost.
Formula
Worked example
A 1200 W appliance on a 120 V DC or unity-power-factor AC outlet: I = 1200 ÷ 120 = 10 A. A 10 kW three-phase motor at 400 V line-to-line with a 0.9 power factor draws 10000 ÷ (1.732 × 0.9 × 400) ≈ 16.0 A.
How to convert watts to amps
Electrical power, current and voltage are linked by the power equation P = V × I, where P is power in watts, V is voltage in volts and I is current in amperes. Rearranging for current gives I = P ÷ V, so you find amps by dividing the wattage by the supply voltage. For a 60-watt bulb on a 120-volt circuit the current is 60 ÷ 120 = 0.5 amps. This direct division holds for any direct-current (DC) circuit and for a single-phase alternating-current (AC) circuit whose power factor is one, which covers most resistive household loads such as heaters, kettles and incandescent lighting. Pick the circuit type at the top, set the power and voltage in any common unit, and the calculator returns the current in both amps and milliamps.
Single phase, three phase and power factor
Alternating-current loads with a power factor below one draw more current than watts ÷ volts alone suggests, because some of the current is reactive and does no real work. For single-phase AC the true current is watts ÷ (volts × power factor), and the calculator also reports the apparent power in volt-amperes, which is the real power divided by the power factor. Three-phase systems add a factor that depends on how the voltage is measured: with line-to-line voltage the current is watts ÷ (√3 × power factor × volts), and with line-to-neutral (phase) voltage it is watts ÷ (3 × power factor × volts). Resistive loads have a power factor of one, while motors, transformers and electronics typically run between 0.7 and 0.95, so always confirm the circuit type and power factor before sizing wire or breakers.
Estimating the running cost
Knowing the current is only half the picture; the running cost depends on energy, which is power multiplied by time. Turn on the running-cost estimate, enter how many hours the load runs each day and your electricity rate per kilowatt-hour, and the calculator multiplies the power in kilowatts by the hours to get daily energy, then by the rate to get the daily and yearly cost. A 1200-watt load running four hours a day uses 4.8 kWh per day; at a rate of 0.17 per kWh that is about 0.82 per day and roughly 298 per year. These figures are planning estimates, since real tariffs, standing charges and duty cycles vary.
Watts to amps at common voltages
| Power (W) | 12 V | 120 V | 240 V |
|---|---|---|---|
| 100 | 8.33 | 0.83 | 0.42 |
| 500 | 41.67 | 4.17 | 2.08 |
| 1000 | 83.33 | 8.33 | 4.17 |
| 1500 | 125.00 | 12.50 | 6.25 |
| 2400 | 200.00 | 20.00 | 10.00 |
Current draw (amps) for a given power at typical DC and single-phase AC voltages, power factor 1.
Frequently asked questions
How many amps is 1000 watts?
It depends on the voltage. At 120 volts, 1000 watts draws 1000 ÷ 120 ≈ 8.33 amps; at 240 volts it draws 1000 ÷ 240 ≈ 4.17 amps; and at 12 volts it draws about 83.3 amps. These assume DC or single-phase AC at a power factor of 1.
Does this formula work for AC and DC?
Yes. For DC and single-phase AC at a power factor of 1, amps = watts ÷ volts. For single-phase loads with a lower power factor, divide by volts × power factor. For three-phase AC, divide by √3 × power factor × line-to-line volts, or by 3 × power factor × line-to-neutral volts. Just choose the circuit type at the top.
What is the power factor and when do I need it?
Power factor is the ratio of real power to apparent power for an AC load. Purely resistive loads (heaters, incandescent bulbs) have a power factor of 1, so it can be ignored. Motors and electronics often run 0.7 to 0.95, drawing more current than watts ÷ volts alone suggests. It does not apply to DC circuits.
What is the difference between line-to-line and line-to-neutral voltage?
In a three-phase system the line-to-line voltage is measured between any two phases, while the line-to-neutral (phase) voltage is measured between one phase and neutral, and is √3 times smaller. The two formulas, √3 × power factor × V for line-to-line and 3 × power factor × V for line-to-neutral, give the same current as long as you use the matching voltage.
How much does it cost to run a 1200 W appliance?
Multiply the power in kilowatts by the hours of use to get energy in kilowatt-hours, then by your rate. A 1200-watt load (1.2 kW) running 4 hours a day uses 4.8 kWh per day; at 0.17 per kWh that is about 0.82 per day and roughly 298 per year. Turn on the running-cost estimate to do this automatically.