Watts to amps calculator
To convert watts to amps, divide by the voltage: 1,500 watts at 120 volts is 12.5 amps. The table below gives the same 1,500 W at 12 V, 240 V, 208 V three-phase and other common supplies.
Notice: For general informational purposes only; not electrical or engineering advice. Work on electrical circuits can cause fire, electric shock or death. Mains-voltage work must comply with the applicable electrical code and be performed by a licensed electrician.
Current
- Voltage Given.
- 120 V
- Current I = P / V = 1,500 W / 120 V.
- 12.5 A
- Resistance R = V² / P = (120 V)² / 1,500 W.
- 9.6 Ω
- Real power Given.
- 1,500 W
- Apparent power V x I, before the power factor. Wiring, breakers and transformers carry this, not the watts.
- 1,500 VA
| Supply | Circuit | Current |
|---|---|---|
| 12 V | DC | 125 A |
| 24 V | DC | 62.5 A |
| 120 V | single-phase | 12.5 A |
| 230 V | single-phase | 6.522 A |
| 240 V | single-phase | 6.25 A |
| 208 V | three-phase | 4.164 A |
| 480 V | three-phase | 1.804 A |
- Ohm's law holds for resistors, heating elements and wire at a fixed temperature. It does not describe LEDs, diodes, batteries or motors, whose current is not proportional to the voltage across them.
- A conductor's resistance rises as it heats, so the cold resistance a meter reads across a lamp filament or heater element is lower than its resistance in use.
- Single-phase AC with a power factor: real power is V x I x pf. The current a breaker and wire see is set by the apparent power, which is why a low power factor needs bigger wiring for the same watts.
How the Ohm's Law Calculator works
Amps = watts / volts. That is the whole conversion on DC and on AC into a resistive load such as a heater, a kettle or a toaster. A 1,500 W space heater on a 120 V outlet draws 1,500 / 120 = 12.5 A. The same heater built for 240 V draws 6.25 A, which is why large appliances are wired for 240 V: half the current for the same power, so thinner wire and less loss in it.
There is no fixed number of amps in a watt. A watt is a rate of energy and an amp is a flow of charge, and the voltage is what links them: the same 12.5 A carries 150 W at 12 V and 1,500 W at 120 V. A conversion that does not ask for the voltage is assuming one.
On AC with a power factor. Motors, compressors, fluorescent and LED drivers and computer power supplies draw current that is partly out of step with the voltage. The formula becomes amps = watts / (volts x power factor). A 1,500 W load with a power factor of 0.85 on 120 V draws 1,500 / (120 x 0.85) = 14.71 A. The breaker and the wire see the 14.71 A, not the 12.5 A the watts alone suggest. Most appliance labels give watts; if a label gives volt-amps (VA), amps = VA / volts with no power factor needed.
On three-phase. amps = watts / (1.732 x volts x power factor), with the line-to-line voltage. 10 kW at 480 V and a power factor of 0.85 is 10,000 / (1.732 x 480 x 0.85) = 14.15 A in each line. At 208 V the same 10 kW, also at 0.85, is 32.66 A. The two classic errors are leaving out the 1.732, which overstates the current by 73%, and using the line-to-neutral voltage (277 or 120), which overstates it the same way.
Motor nameplates. A motor's rated power is its mechanical output at the shaft. The electrical input is larger by the motor's efficiency, so dividing the output watts by the voltage understates the current; use the full-load amps printed on the nameplate where there is one.
What the answer is not. The current a load draws is not the size of breaker it needs. Breaker and wire sizing follow the electrical code's rules for continuous loads and conductor ampacity, which this calculator does not apply.
Ohm's Law Calculator FAQ
How many amps is 1,500 watts?
At 120 V, 1,500 / 120 = 12.5 A. At 240 V it is 6.25 A, and at 12 V DC it is 125 A. The answer always depends on the voltage.
What is the formula for watts to amps?
DC and resistive AC: amps = watts / volts. AC with a power factor: amps = watts / (volts x pf). Three-phase: amps = watts / (1.732 x line-to-line volts x pf).
How many amps is 1,000 watts at 120 volts?
1,000 / 120 = 8.33 A for a resistive load. With a power factor of 0.9 it is 1,000 / (120 x 0.9) = 9.26 A.
Why do I need the voltage to convert watts to amps?
Because watts are volts times amps, the power form of Ohm's law. The same power can be a large current at a low voltage or a small one at a high voltage, so without the voltage the conversion has no single answer.