Free Watts to amps calculator
Enter the power in watts, the voltage, and the circuit type — DC, AC single-phase, or AC three-phase — and this calculator returns the current in amps using A = W / V (and the power factor and √3 for AC), updated live, as you type.
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Estimates from the values you enter. Size breakers and wire to your local electrical code.
Results are estimates. Consult a professional.
How the watts-to-amps calculator works
Watts measure power — how fast energy is used. Amps measure current — how much charge flows each second. You cannot convert one to the other without a voltage, because the same power can flow as a large current at a low voltage or a small current at a high voltage. This calculator takes the power in watts, the voltage in volts, and the circuit type, and returns the current in amps.
DC vs AC single-phase vs three-phase
The same watts draw a different current depending on the circuit. Picking the wrong type is the most common reason a watts-to-amps answer comes out wrong, so set it before you read the result.
DC — A = W / V
Direct current flows one way at a steady voltage: batteries, solar panels, USB and automotive 12 V systems. There is no power factor, so the current is simply the power divided by the voltage. A 60 W load on a 12 V battery draws 5 A.
AC single-phase — A = W / (PF × V)
Single-phase AC is what feeds homes and most plug-in appliances (120 V or 230 V depending on the country). The power factor enters here: a reactive load such as a motor draws more current than its watts alone suggest, so dividing by the power factor raises the current.
AC three-phase — A = W / (√3 × PF × V_line)
Three-phase AC powers industrial and commercial equipment — large motors, HVAC and machine tools. Three live conductors share the load, so for the same watts and line voltage each conductor carries less current than a single-phase circuit would. The √3 factor (about 1.732) captures that sharing. Always use the line-to-line voltage, not the phase voltage.
What power factor is and why it matters
Power factor (PF) is the ratio of real power, measured in watts, to apparent power, measured in volt-amps (VA). It runs from 0 to 1. A purely resistive load — a heater, an incandescent bulb, a kettle — has a power factor of 1, so its watts and volt-amps are equal. Motors, transformers and many electronic supplies are reactive: part of the current goes back and forth without doing useful work, so the power factor falls below 1.
Because current depends on apparent power, a lower power factor means more current for the same watts. At PF 0.8 a load draws 25% more current than its watts suggest (1 ÷ 0.8 = 1.25). That is why the conductor and breaker must be sized from the current, not from the watts.
A worked example converting watts to amps
Marisol has a 1200 W appliance and a 120 V supply. She wants the current draw so she can pick the right breaker — first as a simple resistive (DC-equivalent) load, then as a motor with a power factor of 0.9.
Step 1 — DC or resistive: A = W / V
With no power factor to worry about, A = 1200 ÷ 120 = 10 A. A purely resistive 1200 W load at 120 V draws exactly 10 amps.
Step 2 — AC single-phase with power factor 0.9
Now A = W / (PF × V) = 1200 ÷ (0.9 × 120) = 1200 ÷ 108 = 11.11 A. The lower power factor pushes the current up by about 11% over the resistive case.
Step 3 — three-phase, for comparison
A bigger 10,000 W three-phase load on a 208 V line at PF 0.9 draws A = 10000 ÷ (√3 × 0.9 × 208) = 30.84 A per conductor — far less than the same watts would pull single-phase.
Watts-to-amps quick-reference table
Common power-and-voltage pairs and the current they draw. AC figures assume a power factor of 1 unless noted; lower the power factor and the current rises proportionally.
| Power | Voltage | Type | Current |
|---|---|---|---|
| 60 W | 12 V | DC | 5.00 A |
| 100 W | 120 V | DC / resistive | 0.83 A |
| 1200 W | 120 V | DC / resistive | 10.00 A |
| 1200 W | 120 V | AC 1φ, PF 0.9 | 11.11 A |
| 1500 W | 230 V | AC 1φ, PF 1 | 6.52 A |
| 3000 W | 230 V | AC 1φ, PF 0.85 | 15.35 A |
| 10000 W | 208 V | AC 3φ, PF 0.9 | 30.84 A |
Computed from A = W / V (DC), A = W / (PF × V) (AC 1φ) and A = W / (√3 × PF × V_line) (AC 3φ). Three-phase uses line-to-line voltage.
Why this matters: sizing breakers and wire
Current, not power, is what heats a conductor and what a breaker trips on. Converting watts to amps is the first step in choosing a wire gauge and an overcurrent device that are safe for the load.
- Breaker rating — the breaker must carry the load current without nuisance tripping, yet trip before the wire overheats. Knowing the amps is the starting point.
- Wire gauge — a conductor has an ampacity (a safe current limit) set by its size and insulation. Undersized wire overheats; the amps tell you the minimum gauge.
- Continuous-load margin — many codes require sizing a continuous load (on for 3 hours or more) at 125% of its current, so a 11.11 A load is sized as if it were about 13.9 A.
- Voltage drop on long runs — once you know the current, a voltage drop calculator tells you whether the run is too long for the chosen gauge.
To go the other way — current back to power — use the companion Ohm's law calculator, which also relates voltage, resistance and power.
Common mistakes converting watts to amps
- Forgetting the power factor on AC — using A = W / V for a motor undercounts the current. Reactive loads draw more amps than their watts alone imply.
- Using phase voltage for three-phase — the formula needs the line-to-line voltage. Plugging in the phase voltage gives a current that is too high by √3.
- Confusing watts with volt-amps — equipment is often rated in VA (apparent power). VA already includes the power factor, so do not divide by it again.
- Sizing wire straight from the calculated amps — apply the code's continuous-load margin and derating factors first; the bare current is a minimum, not the final figure.
- Assuming the supply voltage is exact — nominal 120 V or 230 V sags under load. For a worst-case current, use the lowest expected voltage.
How accurate is this watts-to-amps calculator
The arithmetic is exact. For the power, voltage, circuit type and power factor you enter, the calculator returns the current to full floating-point precision using A = W / V (DC), A = W / (PF × V) (single-phase) and A = W / (√3 × PF × V_line) (three-phase).
Real circuits vary for physical reasons, not arithmetic ones. The nominal voltage sags under load, the power factor shifts as a motor's load changes, and ratings carry tolerances. Treat the result as a design figure: apply your local electrical code's margins for continuous loads, ambient temperature and conductor bundling before choosing a breaker or wire. For the underlying relations, the Wikipedia "AC power" article gives the full derivation.
Frequently asked questions about the free Watts to amps calculator
About this Watts to amps calculator
This calculator runs entirely in your browser — nothing you enter is sent anywhere. It converts power in watts to current in amps using A = W / V for DC, A = W / (PF × V) for AC single-phase, and A = W / (√3 × PF × V_line) for AC three-phase, updating the moment you change a value.
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