Amps to Watts Calculator
Amps times volts gives you watts: watts = amps × volts. So 15 amps on a 120-volt circuit is 1,800 watts — but the safe continuous limit is lower (see below).
Voltage
1500 watts
12.5 amps at 120 volts is about 1500 watts.
Runs in your browser — nothing is sent anywhere. Estimates assume nominal voltage and ideal conditions; confirm with a licensed electrician and local code before sizing wire or breakers.
What each breaker can safely carry
The raw rating vs. the safe continuous load (the 80% rule — what actually keeps the breaker from tripping on a load running 3+ hours).
| Breaker | Watts @120V | Watts @240V | Safe continuous @120V |
|---|---|---|---|
| 15 A | 1,800 W | 3,600 W | 1,440 W |
| 20 A | 2,400 W | 4,800 W | 1,920 W |
| 30 A | 3,600 W | 7,200 W | 2,880 W |
| 40 A | 4,800 W | 9,600 W | 3,840 W |
| 50 A | 6,000 W | 12,000 W | 4,800 W |
The formula
Multiply the amps by the voltage. Watts = Amps × Volts. (For a motor, multiply by the power factor too.)
Example: A 20-amp circuit at 120 volts: 20 × 120 = 2,400 watts of capacity — but plan for about 1,920W continuous (the 80% rule).
One caveat that keeps people safe: This is a guide for estimation only. Conversions assume nominal voltage and ideal conditions; real installations vary with power factor, voltage drop, temperature, wire type, and continuous vs. brief use. It doesn't replace the National Electrical Code or a licensed electrician — always confirm with a pro and local code before sizing wire, breakers, or circuits.
Hiring out the wiring?
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Verify a contractor's license by state →Common questions
- How many watts can a 15 amp breaker handle?
- A 15-amp circuit at 120V is 1,800 watts at full rating — but only about 1,440 watts continuously (3+ hours), because of the NEC 80% rule. Design to 1,440W to avoid nuisance trips.
- How many watts is 20 amps?
- 2,400 watts at 120V (20 × 120), or 4,800 watts at 240V. The safe continuous figure is ~1,920W at 120V.
- Why is the 'safe' number lower than amps × volts?
- Breakers aren't built to hold their full rating indefinitely. The 80% rule means a continuous load should stay under 80% of the breaker's amps — that's the number that actually prevents tripping and overheating.
- Does power factor matter here?
- For resistive loads, no. For motors and other inductive loads the real watts are amps × volts × power factor (often ~0.8), so the same amps deliver fewer real watts.