Watts to Amps Calculator
5,000 W at 240 V is 20.8 A.
- Current
- 20.83 A
- 125% for continuous loads
- 26.04 A
To convert watts to amps, divide the watts by the voltage: I = P ÷ V. A 1,500 W heater on 120 V draws 12.5 A. For AC motors and other inductive loads, also divide by the power factor, and for three-phase circuits divide by √3 (1.732) as well.
Enter the power in watts, the voltage and the circuit type. Add the power factor from the nameplate for motors, compressors and drivers (use 1.0 for heaters, incandescent lights and other resistive loads).
Inputs explained
- Watts (P): real power from the nameplate or spec sheet. If the nameplate gives kVA or VA instead, enter that with a power factor of 1.0, because VA already includes the reactive part.
- Voltage (V): the voltage the load is connected across. For three-phase, use the line-to-line voltage (208, 240 or 480 V), not the line-to-neutral value.
- Circuit type: DC, single-phase AC or three-phase AC.
- Power factor (PF): 1.0 for resistive loads. Motors and older magnetic-ballast lighting run lower; always prefer the nameplate figure to a guess.
Formulas
DC and single-phase AC, resistive load: I = P ÷ V
Single-phase AC with power factor: I = P ÷ (V × PF)
Three-phase AC, line-to-line voltage: I = P ÷ (√3 × V × PF) = P ÷ (1.732 × V × PF)
Where I is current in amps, P is real power in watts, V is voltage and PF is power factor (between 0 and 1). The same relationships, rearranged, are on the Ohm's law calculator.
Worked examples
DC
- 600 W inverter load on a 12 V battery: 600 ÷ 12 = 50 A at the output. Inverters are not 100% efficient; at 90% efficiency the battery side supplies 600 ÷ 12 ÷ 0.9 = 55.6 A. Size the DC cable and fuse for the battery-side current.
Single-phase AC
- 1,500 W space heater at 120 V: 1,500 ÷ 120 = 12.5 A. That is 83% of a 15 A circuit. Cord-and-plug equipment that isn't fastened in place may not exceed 80% of the branch-circuit rating (NEC 210.23(A)(1)), which is 12 A on a 15 A circuit, so it belongs on a 20 A circuit.
- 11,520 W EV charger at 240 V: 11,520 ÷ 240 = 48 A. EV chargers are continuous loads, so the circuit is sized at 125%: 48 × 1.25 = 60 A breaker, with conductors rated for 60 A.
- 1,200 W motor load at 120 V, PF 0.8: 1,200 ÷ (120 × 0.8) = 12.5 A, not the 10 A you get if you ignore power factor.
Three-phase AC
- 10 kW heater at 208 V, PF 1.0: 10,000 ÷ (1.732 × 208 × 1.0) = 27.8 A per phase.
- 15 kW load at 480 V, PF 0.9: 15,000 ÷ (1.732 × 480 × 0.9) = 20.0 A per phase.
- 20 kW load at 208 V, PF 0.85: 20,000 ÷ (1.732 × 208 × 0.85) = 65.3 A per phase.
Motors: don't convert from horsepower with a formula. Use the full-load current from NEC Table 430.248 (single-phase) or 430.250 (three-phase) for sizing conductors and protection.
Watts to amps chart (single-phase, PF 1.0)
| Power | at 120 V | at 240 V |
|---|---|---|
| 100 W | 0.8 A | 0.4 A |
| 500 W | 4.2 A | 2.1 A |
| 1,000 W | 8.3 A | 4.2 A |
| 1,500 W | 12.5 A | 6.2 A |
| 1,800 W | 15.0 A | 7.5 A |
| 2,000 W | 16.7 A | 8.3 A |
| 2,400 W | 20.0 A | 10.0 A |
| 3,000 W | 25.0 A | 12.5 A |
| 3,600 W | 30.0 A | 15.0 A |
| 4,000 W | 33.3 A | 16.7 A |
| 4,800 W | 40.0 A | 20.0 A |
| 5,000 W | 41.7 A | 20.8 A |
| 7,200 W | 60.0 A | 30.0 A |
| 9,600 W | 80.0 A | 40.0 A |
| 10,000 W | 83.3 A | 41.7 A |
| 11,520 W | 96.0 A | 48.0 A |
kW to amps chart (three-phase, PF 1.0)
| Load | at 208 V | at 240 V | at 480 V |
|---|---|---|---|
| 5 kW | 13.9 A | 12.0 A | 6.0 A |
| 10 kW | 27.8 A | 24.1 A | 12.0 A |
| 15 kW | 41.6 A | 36.1 A | 18.0 A |
| 20 kW | 55.5 A | 48.1 A | 24.1 A |
| 30 kW | 83.3 A | 72.2 A | 36.1 A |
| 45 kW | 124.9 A | 108.3 A | 54.1 A |
| 75 kW | 208.2 A | 180.4 A | 90.2 A |
For a power factor below 1.0, divide the table value by the PF.
From amps to breaker and wire size
The current you calculate is the starting point, not the answer:
- Continuous loads (3 hours or more) need a circuit rated at 125% of the load. A 48 A charger needs a 60 A circuit.
- Pick the breaker at or above that value.
- Pick the wire from the ampacity chart for the breaker, then check voltage drop. Use the wire size calculator.
- Add it to the service total. Several large loads on one house or panel need a load calculation, not a sum of breaker sizes.
Common mistakes
- Using 240 V for a 208 V building. A 15 kW three-phase heater draws 41.6 A at 208 V but 36.1 A at 240 V; picking the wrong voltage understates the current by about 13%.
- Applying √3 to a single-phase load on a three-phase system. A 5,000 W water heater connected across two legs of a 208Y/120 V panel is a single-phase load: 5,000 ÷ 208 = 24.0 A, not 13.9 A.
- Ignoring power factor on motors and compressors, which understates the current.
- Sizing from running watts when the nameplate lists a higher current or a minimum circuit ampacity (MCA). The nameplate governs.
Frequently asked questions
How many amps is 1500 watts?
12.5 A at 120 V and 6.25 A at 240 V.
How many amps is 1000 watts?
8.3 A at 120 V and 4.2 A at 240 V.
How many watts can a 15 amp circuit handle?
1,800 W at 120 V maximum, and 1,440 W for a continuous load (80%).
How many watts is 30 amps?
3,600 W at 120 V and 7,200 W at 240 V.
How do I convert kW to amps on three-phase?
Multiply kW by 1,000, then divide by 1.732 × the line-to-line voltage × the power factor. At PF 1.0, 10 kW is 27.8 A at 208 V and 12.0 A at 480 V.
Why does my appliance draw more amps than the calculation?
Motors and compressors draw several times their running current when starting, and many devices have a power factor below 1.0. The nameplate current is the value to use for circuit sizing.
Converting dozens of equipment schedules by hand? SparkQuote reads the loads off your plans and carries the currents into circuit sizing and pricing. See the electrical estimator.
Last updated: October 6, 2026. Results must be checked against the adopted code and the AHJ. Electrical work should be done by qualified people.