Watts to amps formula
DC or AC single-phase: amps = watts ÷ voltage (single-phase AC with a power factor other than 1: amps = watts ÷ (power factor × voltage)). AC three-phase: amps = watts ÷ (√3 × power factor × line-to-line voltage).
- 1500 watts at 120V, single-phase, PF 1: 1500 ÷ 120 = 12.5 A
- 1500 watts at 240V: 1500 ÷ 240 = 6.25 A
- 100 watts at 12V DC: 100 ÷ 12 = 8.33 A
- 10,000 watts at 480V three-phase, PF 0.9: 10,000 ÷ (√3 × 0.9 × 480) = 13.36 A
How many amps is 1500 watts?
At 120V, 1500 watts is 12.5 amps. That's right at the edge of what a standard 15A/120V household circuit is rated for -- and over the 80%-continuous-load guideline for one (12A), so a 1500W continuous load (e.g. a space heater) on a 15A circuit should generally be the only thing on that circuit. At 240V, the same 1500 watts is only 6.25 amps.
Power factor: why it matters
Power factor (PF) is 1 for purely resistive loads (heaters, incandescent lighting) and typically 0.8 to 0.9 for motors and other inductive AC loads (pumps, compressors, some power tools). A lower PF means more current for the same wattage: 1000 watts at 240V is 4.17A at PF 1, but 4.9A at PF 0.85. Check the load's nameplate for its actual power factor; if you don't know it, PF 1 gives a conservative (lower) amps estimate for a resistive load, but may understate current for a motor.
Breaker sizing: the 80% continuous-load rule
The NEC's general continuous-load guidance (sections 210.19(A)(1)(a) and 210.20(A)) says a load running 3 hours or more should not exceed 80% of the breaker/circuit rating. A 12A continuous load therefore calls for at least a 15A breaker (in practice, the next standard size up -- commonly 15A), and a 20A breaker should not carry more than 16A continuously. This is general code guidance, not a substitute for checking your local code or asking a licensed electrician.
Common wattages converted to amps
| Watts | Amps @ 120V | Amps @ 240V |
|---|---|---|
| 100 W | 0.83 A | 0.42 A |
| 250 W | 2.08 A | 1.04 A |
| 500 W | 4.17 A | 2.08 A |
| 1,000 W | 8.33 A | 4.17 A |
| 1,500 W | 12.5 A | 6.25 A |
| 2,000 W | 16.67 A | 8.33 A |
| 3,000 W | 25 A | 12.5 A |
| 5,000 W | 41.67 A | 20.83 A |
Single-phase AC, power factor 1 (purely resistive). Use the calculator above for DC, three-phase or a different power factor.
More electrical & energy tools
- Amps to watts calculator: the reverse conversion, plus 15A/20A circuit wattage.
- Voltage drop calculator: check how much voltage a wire run loses at that current.
- Electricity cost calculator: turn watts and hours of use into a dollar cost.
Frequently asked questions
How many amps is 1500 watts?
At 120V (a standard US household outlet), 1500 watts is 12.5 amps (1500 ÷ 120). At 240V it's 6.25 amps (1500 ÷ 240) -- the same power draws half the current at double the voltage.
How do I convert watts to amps?
For DC or AC single-phase: amps = watts ÷ voltage (or watts ÷ (power factor × voltage) for AC with a power factor other than 1). For AC three-phase: amps = watts ÷ (√3 × power factor × line-to-line voltage). Example: 1000 watts at 120V, single-phase, power factor 1: 1000 ÷ 120 = 8.33 amps.
How many amps is 1000 watts?
At 120V: 1000 ÷ 120 = 8.33 amps. At 240V: 1000 ÷ 240 = 4.17 amps.
What is power factor and why does it matter for this conversion?
Power factor (PF) measures how efficiently an AC load uses current; it's 1 for purely resistive loads (heaters, incandescent bulbs, most electronics power supplies rated for it) and typically 0.8-0.9 for motors and other inductive loads. A lower power factor means MORE amps for the same watts: 1000 watts at 240V and PF 1 is 4.17A, but at PF 0.85 it's 4.9A. If you don't know a device's power factor, check its nameplate or leave it at 1 for a resistive-load estimate.
Does DC use the same formula as AC?
DC uses the simplest form: amps = watts ÷ volts, with no power factor. For example, 100 watts at 12V DC (a common solar/RV/automotive voltage) is 100 ÷ 12 = 8.33 amps -- notice how much higher the current is than the same wattage at 120V, which is why low-voltage systems need thicker wire for the same load.
How is three-phase different?
Three-phase power splits current across three conductors, so for the same power the amps per conductor are lower than single-phase. The formula is amps = watts ÷ (√3 × power factor × line-to-line voltage). Example: 10,000 watts at 480V line-to-line, power factor 0.9: 10,000 ÷ (√3 × 0.9 × 480) = 13.36 amps.
What size breaker do I need for a continuous load?
The NEC's general continuous-load guidance (210.19(A)(1)(a) / 210.20(A)) is not to load a breaker beyond 80% of its rating for a load running 3 hours or more, i.e. the breaker should be at least the continuous amps ÷ 0.8. A 12A continuous load calls for at least a 15A breaker (commonly a standard 15A breaker); a 20A breaker in turn should not carry more than 16A continuously. This is general guidance, not a substitute for your local code or an electrician.
Is amps the same as watts?
No -- watts measure power (the rate of energy use), while amps measure current (the rate of electric charge flow). They're related by voltage: watts = volts × amps (times power factor for AC), which is exactly what this calculator solves for amps.
Why do the same watts need more amps at a lower voltage?
Because amps = watts ÷ voltage: for a fixed amount of power, current is inversely proportional to voltage. That's why 12V and 24V systems (solar, RV, automotive) need much heavier wire than a 120V or 240V circuit carrying the same wattage -- the current, and the voltage drop and heating that go with it, are much higher.
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