Watts to Amps Calculator
Enter power, voltage and circuit type to get current in amps. Works for DC, single-phase AC with power factor, and three-phase AC using line-to-line or line-to-neutral voltage.
Watts to amps formulas
Here P is real power in watts, V is voltage in volts, PF is the power factor (between 0 and 1) and I is the current in amps. For a purely resistive load such as a heater, kettle or incandescent lamp, PF is 1 and AC single-phase reduces to the same formula as DC. For motors, compressors and switch-mode supplies, PF is typically 0.8–0.95; check the nameplate when possible.
Worked examples
DC: a 1000 W inverter load on a 120 V DC bus draws I = 1000 / 120 = 8.33 A. The same 1000 W from a 12 V battery is 1000 / 12 = 83.3 A, which is why low-voltage systems need thick cables.
Single-phase AC: a 1500 W space heater on 120 V (PF 1) draws 1500 / 120 = 12.5 A. As a continuous load it needs a breaker of at least 12.5 / 0.8 = 15.6 A, so a 20 A circuit.
Three-phase AC: a 10 kW motor load on 480 V line-to-line with PF 0.9 draws I = 10,000 / (1.732 × 480 × 0.9) = 13.36 A per line. If you only know the 277 V line-to-neutral voltage, I = 10,000 / (3 × 277 × 0.9) = 13.37 A — the same within rounding, because 480 ≈ √3 × 277.
Watts to amps reference table
| Power | 12 V DC | 120 V 1φ | 240 V 1φ | 208 V 3φ | 480 V 3φ |
|---|---|---|---|---|---|
| 100 W | 8.33 A | 0.83 A | 0.42 A | 0.28 A | 0.12 A |
| 500 W | 41.67 A | 4.17 A | 2.08 A | 1.39 A | 0.60 A |
| 1,000 W | 83.33 A | 8.33 A | 4.17 A | 2.78 A | 1.20 A |
| 1,500 W | 125.00 A | 12.50 A | 6.25 A | 4.16 A | 1.80 A |
| 2,000 W | 166.67 A | 16.67 A | 8.33 A | 5.55 A | 2.41 A |
| 3,000 W | 250.00 A | 25.00 A | 12.50 A | 8.33 A | 3.61 A |
| 5,000 W | 416.67 A | 41.67 A | 20.83 A | 13.88 A | 6.01 A |
| 10,000 W | 833.33 A | 83.33 A | 41.67 A | 27.76 A | 12.03 A |
PF = 1. For other power factors divide the current by PF.
Breaker sizing note (80% rule)
The calculator reports the minimum breaker size for a continuous load as I / 0.8 and the next common standard rating (15, 20, 25, 30, 40, 50, 60 A …). This reflects the NEC guidance that continuous loads should not exceed 80% of an overcurrent device rating. It is informational only: wire gauge, terminal temperature ratings, motor starting current, derating and local amendments all affect the final choice, so confirm with a licensed electrician.
Common mistakes
- Using kVA instead of kW. Apparent power (VA) already includes the power factor; divide VA by V (or √3·V) directly.
- Using the phase voltage with the √3 formula. 208 V and 480 V are line-to-line; 120 V and 277 V are line-to-neutral.
- Ignoring efficiency. A motor's shaft power in horsepower or kW is output; electrical input = output / efficiency.
Frequently asked questions
How many amps is 1000 watts?
At 120 V, 1000 W draws 8.33 A (DC or AC with power factor 1). At 240 V it is 4.17 A, and at 12 V DC it is 83.3 A.
Why does power factor matter?
Motors, transformers and many power supplies draw current that is out of phase with voltage. Real power P = V × I × PF, so for the same wattage a lower power factor means more current. A PF of 0.8 draws 25% more current than a PF of 1.
Should I use line-to-line or line-to-neutral voltage for three-phase?
Use whichever voltage you know. With line-to-line voltage (e.g. 208 V or 480 V) the current is P / (√3 × V × PF). With line-to-neutral voltage (e.g. 120 V or 277 V) it is P / (3 × V × PF). Both give the same answer for the same system.
What is the 80% breaker rule?
In the US NEC, continuous loads (running three hours or more) should not exceed 80% of the breaker rating, so the breaker should be at least 125% of the continuous current. This calculator shows that figure for information only; conductor sizing, ambient temperature and local code also apply.
Can I convert watts to amps without knowing voltage?
No. Current depends on voltage: I = P / V. Pick the supply voltage (for example 120 V household, 12 V automotive, 480 V industrial) to get a result.