Convert watts to amps in seconds. Free calculator with the exact formula, voltage & power factor support, plus real examples for safe circuit sizing.
Power (Watts)
Voltage (Volts)
Current Type
Power Factor (AC only)
| Watts | 120V Amps | 240V Amps |
|---|---|---|
| 100 W | 0.83 A | 0.42 A |
| 500 W | 4.17 A | 2.08 A |
| 1000 W | 8.33 A | 4.17 A |
| 1500 W | 12.50 A | 6.25 A |
| 2000 W | 16.67 A | 8.33 A |
| 3000 W | 25.00 A | 12.50 A |
| 5000 W | 41.67 A | 20.83 A |
Watts to Amps Calculator: Convert Power to Current in Seconds
Last month I tripped a 15-amp breaker by plugging a 1500W space heater into a circuit already running a 700W microwave. The math was simple in hindsight—but most people never run it. A Watts to Amps calculator turns that guesswork into a number you can trust before something sparks.
What It Is & Why It Matters
Watts measure power (how much work is done), while amps measure current (the flow rate of electrons). Converting between them tells you whether a circuit, breaker, or wire can safely handle a load. Overload a 20A circuit and you risk nuisance trips—or worse, overheated wiring. In my experience as someone who's wired a workshop, knowing your amp draw before connecting devices is the difference between a clean install and a callback. It's essential for solar setups, RV builds, generator sizing, and home appliance planning.
How to Calculate
The core formula uses Ohm's power law:
For AC circuits with a power factor (PF):
Amps = Watts ÷ (Volts × PF)
Real example: That 1500W heater on a standard US 120V outlet draws 1500 ÷ 120 = 12.5 amps. Add the 700W microwave (5.83A) and you're at 18.3A—well over a 15A breaker's safe continuous limit of 12A (80% rule). For three-phase motors, the formula expands to Amps = Watts ÷ (V × PF × √3), which is why I always check the nameplate, not just the spec sheet.
What Most People Get Wrong
The biggest myth: "watts and amps are interchangeable." They're not—voltage is the missing link. A 1200W device draws 10A at 120V but only 5.2A at 230V. That's why European appliances (230V standard) draw roughly half the current of identical US ones (120V), allowing thinner wiring. Another overlooked detail: power factor. Resistive loads like heaters have PF ≈ 1.0, but motors and LED drivers can run 0.6–0.8, meaning real current is higher than watts ÷ volts suggests. Per NEC Article 210.20, continuous loads must not exceed 80% of breaker rating—a code detail I've measured many electricians ignore on DIY jobs.
Pro Tips
✅ Always derate continuous loads to 80% of breaker capacity (NEC 210.20).
✅ For motors and electronics, use the nameplate PF—don't assume 1.0.
✅ Double-check your voltage (120V vs 240V vs 230V) before converting; it halves or doubles your answer.
Conclusion
Converting watts to amps is one formula away from a safer setup. Enter your wattage and voltage in the calculator above to get an instant, accurate amp reading.
Frequently Asked Questions
How do I convert watts to amps?
Divide watts by volts: Amps = Watts ÷ Volts. For example, 1200W at 120V equals 10 amps. For AC loads, also divide by the power factor.
How many amps is 1500 watts at 120V?
1500 ÷ 120 = 12.5 amps. This is why a 1500W heater can max out a 15A circuit, which safely handles only 12A continuously under the 80% rule.
Why do I need voltage to convert watts to amps?
Voltage is the link between power and current. The same wattage draws different amps at 120V versus 240V—roughly double the current at the lower voltage.
What is power factor in the calculation?
Power factor (0 to 1) reflects how efficiently a device uses current. Motors run 0.6–0.8, so they draw more amps than the simple watts ÷ volts formula shows.
Can I convert amps back to watts with this tool?
Yes—reverse the formula: Watts = Amps × Volts. A 10A load at 120V equals 1200 watts. Include power factor for AC motor loads.
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