Energy use and cost
Watts to amps calculator
Amps = watts ÷ volts, and watts = amps × volts (for motors and electronics, multiply by the power factor too). 1,500 W at 120 V is 12.5 A; the same 1,500 W at 240 V is 6.25 A.
12.50 Afrom 1,500 W at 120 V
- Watts
- 1,500 W = 1.50 kW
- Amps
- 12.50 A
- Power factor
- 1.00
- Breaker if it runs 3 h or more
- 20 A
Watts to amps formula
watts = volts × amps × power factor amps = watts ÷ (volts × power factor) kW = watts ÷ 1,000
For resistive loads (heaters, incandescent bulbs, toasters) power factor is 1 and watts = volts × amps exactly. For motors and many electronics, current and voltage are out of step, so the "apparent power" (volt-amps, VA) is higher than the real power (watts). Generators and UPSs are rated both ways: a "1,500 VA / 900 W" UPS means a power factor of 0.6.
Watts to amps table
| Watts | Amps @ 120 V | Amps @ 240 V | Amps @ 12 V DC |
|---|---|---|---|
| 100 | 0.83 | 0.42 | 8.3 |
| 500 | 4.17 | 2.08 | 41.7 |
| 1,000 | 8.33 | 4.17 | 83.3 |
| 1,500 | 12.50 | 6.25 | 125.0 |
| 2,000 | 16.67 | 8.33 | 166.7 |
| 3,000 | 25.00 | 12.50 | 250.0 |
| 5,000 | 41.67 | 20.83 | 416.7 |
| 7,500 | 62.50 | 31.25 | 625.0 |
| 10,000 | 83.33 | 41.67 | 833.3 |
How many watts a breaker carries
The 80% column is the limit for continuous loads (three hours or more) under NEC 210.20(A).
| Breaker | Watts @ 120 V | 80% continuous | Watts @ 240 V | 80% continuous |
|---|---|---|---|---|
| 15 A | 1,800 | 1,440 | 3,600 | 2,880 |
| 20 A | 2,400 | 1,920 | 4,800 | 3,840 |
| 30 A | 3,600 | 2,880 | 7,200 | 5,760 |
| 40 A | 4,800 | 3,840 | 9,600 | 7,680 |
| 50 A | 6,000 | 4,800 | 12,000 | 9,600 |
| 60 A | 7,200 | 5,760 | 14,400 | 11,520 |
Common questions
How many amps is 1,500 watts?
12.5 A at 120 V, 6.25 A at 240 V.
How many watts is 30 amps?
3,600 W at 120 V and 7,200 W at 240 V. A 30 A, 240 V generator inlet (L14-30) therefore carries up to 7,200 W.
Why is my 240 V appliance fewer amps?
Same power, double the voltage, half the current. That is why big loads like dryers, ranges and EV chargers run at 240 V: smaller wire for the same power.