Watts to Amps Calculator
Your estimate
- Apparent power
- 1,500 VA1.5 kVA
- Breaker size
- 20 A
- Copper wire for that breaker
- 12 AWG
Amps from watts and volts — and the breaker and wire that load needs.
Updated 2026-10-20 · Based on: Ohm’s law, NEC Chapter 9 Table 8, 210.20 and 310.16; DIN VDE 0100-520 for metric.
How to use the Watts to Amps Calculator
- Enter the power of the appliance or load in watts (it is on the label or in the manual).
- Enter the voltage: 120 V for a US outlet, 240 V for a dryer or range, 12 V or 24 V for DC.
- Choose single phase, three phase or DC. For motors and other inductive loads enter the power factor (0.8–0.95); heaters and lights are 1.
- Read the amps, the breaker size for a continuous load and the copper wire for that breaker.
Formula
DC: amps = watts ÷ volts. AC single phase: amps = watts ÷ (volts × power factor).
AC three phase: amps = watts ÷ (√3 × line-to-line volts × power factor), with √3 ≈ 1.732.
Breaker: a continuous load (3 hours or more) may use only 80 % of the breaker, so the breaker must be at least 125 % of the current (NEC 210.20). Wire: the smallest copper size whose 75 °C ampacity covers that breaker (NEC 310.16 and 240.4(D)).
Worked example
With the values preset in the calculator above:
- Power
- 1,500 W
- Voltage
- 120 V
- Phase
- Single phase
- Power factor (AC)
- 1
- Current
- 12.5 A
- Apparent power
- 1,500 VA (1.5 kVA)
- Breaker size
- 20 A
- Copper wire for that breaker
- 12 AWG
How to convert watts to amps
Divide the watts by the volts. A 1,500 W space heater on a 120 V outlet draws 12.5 A. The same heater on 240 V draws 6.25 A, half the current, which is why big appliances run on 240 V.
For AC motors, compressors and power supplies, the current also depends on the power factor. A 1,000 W load with a power factor of 0.8 draws 10.42 A at 120 V, not 8.33 A.
How many amps is 1,000, 1,500 or 2,000 watts?
- 1,000 W at 120 V = 8.33 A; at 240 V = 4.17 A.
- 1,500 W at 120 V = 12.5 A — the most a plug-in heater can use on a 15 A circuit.
- 2,000 W at 120 V = 16.67 A; at 240 V = 8.33 A.
- 3,000 W at 240 V = 12.5 A. 5,000 W at 240 V = 20.83 A.
- 100 W at 12 V DC = 8.33 A — size 12 V wiring for that much current.
What size breaker do I need?
Breakers are sized for the current, not the watts. For a load that runs three hours or more, keep it at 80 % of the breaker: a 15 A circuit carries 12 A (1,440 W at 120 V) continuously, a 20 A circuit 16 A (1,920 W). Use the wire size calculator for long runs, where voltage drop may call for a bigger wire.
Watts to amps chart (120 V)
| Power | Current |
|---|---|
| 100 | 0.83 A |
| 500 | 4.17 A |
| 1,000 | 8.33 A |
| 1,500 | 12.5 A |
| 1,800 | 15 A |
| 2,000 | 16.67 A |
| 3,000 | 25 A |
| 5,000 | 41.67 A |
Frequently asked questions
How many amps is 1,500 watts?
12.5 A at 120 V and 6.25 A at 240 V.
How many watts can a 15 amp circuit handle?
1,800 W at 120 V in total, and 1,440 W for a load that runs continuously (80 %).
How many amps does a 5,000 watt generator produce?
About 20.83 A at 240 V or 41.67 A at 120 V.
Watts to amps at 12 volts?
Divide by 12: a 300 W inverter load draws 25 A from a 12 V battery (more, once inverter losses are added).
Why do I need the power factor?
On AC, motors and electronics draw current that does no work. Real power (W) = volts × amps × power factor, so a lower power factor means more amps for the same watts.
More calculators
Estimates only — check quantities with your supplier and local building code before you order.